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50 Best Evolutionary Psychology Research Topics

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Best Evolutionary Psychology Research Topics

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  • Evolutionary psychology perspective: Why do people cry?
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  • Application of evolutionary psychology in marketing
  • Correlation between evolutionary psychology and gender roles
  • An evolutionary perspective on generational culture
  • Evolutionary psychology perspective on child development
  • Evolutionary psychology perspective on human social strategies
  • Correlation between aesthetics and evolutionary psychology

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  • Charles Darwin’s perspective on evolutionary psychology
  • Evolutionary psychology and animal behavior
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  • Evolutionary psychology perspective on religion
  • History, current status, and future of evolutionary psychology
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  • Is evolutionary psychology possible?
  • The evolutionary psychology of eating habits and food choice

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  • Psychological impacts of food inequality
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  • The future of evolutionary psychology on human partnerships
  • Evolutionary psychology perspective on human behavior: Consumer brand choice selection
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  • Evolutionary psychology model of understanding terrorism
  • Evolutionary psychology perspective on social media: Psychology of terrorism

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  • Behavioral immune system: History, current concerns, and future
  • Evolutionary psychology modern criticism
  • Evolutionary psychology perspective on adaptations to predators and prey
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  • Evolutionary psychology: A quest to understanding human nature
  • Evolutionary psychology: Adaptations to dangers from human
  • Evolutionary psychology: The origin of the phobia
  • How culture and childhood environment creates an unpredictable adulthood personality
  • How does the behavioral immune system impact responses to COVID-19 threats?
  • Implications of evolutionary psychology for behavior therapy

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  • Ethics of evolutionary psychology
  • Evolutionary perspective: Evolution of narcissism
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  • The evolutionary psychology of mate selection in your country
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Evolutionary Psychology

Evolutionary psychology is one of many biologically informed approaches to the study of human behavior. Along with cognitive psychologists, evolutionary psychologists propose that much, if not all, of our behavior can be explained by appeal to internal psychological mechanisms. What distinguishes evolutionary psychologists from many cognitive psychologists is the proposal that the relevant internal mechanisms are adaptations—products of natural selection—that helped our ancestors get around the world, survive and reproduce. To understand the central claims of evolutionary psychology we require an understanding of some key concepts in evolutionary biology, cognitive psychology, philosophy of science and philosophy of mind. Philosophers are interested in evolutionary psychology for a number of reasons. For philosophers of science —mostly philosophers of biology—evolutionary psychology provides a critical target. Although here is a broad consensus among philosophers of biology that evolutionary psychology is a deeply flawed enterprise, this does not entail that these philosophers completely reject the relevance of evolutionary theory to human psychology. For philosophers of mind and cognitive science evolutionary psychology has been a source of empirical hypotheses about cognitive architecture and specific components of that architecture. However, some philosophers of mind are also critical of evolutionary psychology but their criticisms are not as all-encompassing as those presented by philosophers of biology. Evolutionary psychology is also invoked by philosophers interested in moral psychology both as a source of empirical hypotheses and as a critical target.

In what follows I briefly explain evolutionary psychology’s relations to other work on the biology of human behavior and the cognitive sciences. Next I introduce the research tradition’s key theoretical concepts. In the following section I take up discussions about evolutionary psychology in the philosophy of mind, specifically focusing on the debate about the massive modularity thesis. I go on to review some of the criticisms of evolutionary psychology presented by philosophers of biology and assess some responses to those criticisms. I then go on to introduce some of evolutionary psychology’s contributions to moral psychology and human nature and, finally, briefly discuss the reach and impact of evolutionary psychology.

1. Evolutionary Psychology: One research tradition among the various biological approaches to explaining human behavior

2. evolutionary psychology’s theory and methods, 3. the massive modularity hypothesis, 4. philosophy of biology vs. evolutionary psychology, 5. moral psychology and evolutionary psychology, 6. human nature, 7. applications of evolutionary psychology and prospects for further debate, other internet resources, related entries.

This entry focuses on the specific approach to evolutionary psychology that is conventionally named by the capitalized phrase “Evolutionary Psychology”. This naming convention is David Buller’s (2000; 2005) idea. He introduces the convention to distinguish a particular research tradition (Laudan 1977) from other approaches to the biology of human behavior. [ 1 ] This research tradition is the focus here but lower case is used throughout as no other types of evolutionary psychology are discussed. Evolutionary psychology rests upon specific theoretical principles (presented in section 2 below) not all of which are shared by others working in the biology of human behavior (Laland & Brown 2002; Brown et al. 2011). For example, human behavioral ecologists present and defend explanatory hypotheses about human behavior that do not appeal to psychological mechanisms (e.g., Hawkes 1990; Hrdy 1999). Behavioral ecologists also believe that much of human behavior can be explained by appealing to evolution while rejecting the idea held by evolutionary psychologists that one period of our evolutionary history is the source of all our important psychological adaptations (Irons 1998). Developmental psychobiologists take yet another approach: they are anti-adaptationist. (Michel & Moore 1995; but see Bateson & Martin 1999; Bjorklund & Hernandez Blasi 2005 for examples of developmentalist work in an adaptationist vein.) These theorists believe that much of our behavior can be explained without appealing to a suite of specific psychological adaptations for that behavior. Instead they emphasize the role of development in the production of various human behavioral traits. From here on, “evolutionary psychology” refers to a specific research tradition among the many biological approaches to the study of human behavior.

Paul Griffiths argues that evolutionary psychology owes theoretical debt to both sociobiology and ethology (Griffiths 2006; Griffiths 2008). Evolutionary psychologists acknowledge their debt to sociobiology but point out that they add a dimension to sociobiology: psychological mechanisms. Human behaviors are not a direct product of natural selection but rather the product of psychological mechanisms that were selected for. The relation to ethology here is that in the nineteen fifties, ethologists proposed instincts or drives that underlie our behavior; [ 2 ] evolutionary psychology’s psychological mechanisms are the correlates to instincts or drives. Evolutionary psychology is also related to cognitive psychology and the cognitive sciences. The psychological mechanisms they invoke are computational, sometimes referred to as “Darwinian algorithms” or as “computational modules”. This overt cognitivism sets evolutionary psychology apart from much work in the neurosciences and from behavioral neuroendocrinology. In these fields internal mechanisms are proposed in explanations of human behavior but they are not construed in computational terms. David Marr’s (e.g., 1983) well known three part distinction is often invoked to distinguish the levels at which researchers focus their attention in the cognitive and neurosciences. Many neuroscientists and behavioral neuroendocrinologists work at the implementation level while cognitive psychologists work at the level of the computations that are implemented at the neurobiological level (see Griffiths 2006).

Evolutionary psychologists sometimes present their approach as potentially unifying, or providing a foundation for, all other work that purports to explain human behavior (e.g., Tooby & Cosmides 1992). This claim has been met with strong skepticism by many social scientists who see a role for a myriad of types of explanation of human behavior, some of which are not reducible to biological explanations of any sort. This discussion hangs on issues of reductionism in the social sciences. (Little 1991 has a nice introduction to these issues.) There are also reasons to believe that evolutionary psychology neither unifies nor provides foundations for closely neighboring fields such as behavioral ecology or developmental psychobiology. (See the related discussion in Downes 2005.) In other work, evolutionary psychologists present their approach as being consistent with or compatible with neighboring approaches such as behavioral ecology and developmental psychobiology. (See Buss’s introduction to Buss 2005.) The truth of this claim hangs on a careful examination of the theoretical tenets of evolutionary psychology and its neighboring fields. We now turn to evolutionary psychology’s theoretical tenets and revisit this discussion in section 4 below.

Influential evolutionary psychologists, Leda Cosmides and John Tooby, provide the following list of the field’s theoretical tenets (Tooby & Cosmides 2005):

  • The brain is a computer designed by natural selection to extract information from the environment.
  • Individual human behavior is generated by this evolved computer in response to information it extracts from the environment. Understanding behavior requires articulating the cognitive programs that generate the behavior.
  • The cognitive programs of the human brain are adaptations. They exist because they produced behavior in our ancestors that enabled them to survive and reproduce.
  • The cognitive programs of the human brain may not be adaptive now; they were adaptive in ancestral environments.
  • Natural selection ensures that the brain is composed of many different special purpose programs and not a domain general architecture.
  • Describing the evolved computational architecture of our brains “allows a systematic understanding of cultural and social phenomena” (16–18).

Tenet 1 emphasizes the cognitivism that evolutionary psychologists are committed to. 1 in combination with 2 directs our attention as researchers not to parts of the brain but to the programs run by the brain. It is these programs—psychological mechanisms—that are products of natural selection. While they are products of natural selection, and hence adaptations, these programs need not be currently adaptive. Our behavior can be produced by underlying psychological mechanisms that arose to respond to particular circumstances in our ancestors’ environments. Tenet 5 presents what is often called the “massive modularity thesis” (see, e.g., Samuels 1998; Samuels 2000). There is a lot packed into this tenet and we will examine this thesis in some detail below in section 3. In brief, evolutionary psychologists maintain that there is an analogy between organs and psychological mechanisms or modules. Organs perform specific functions well and are products of natural selection. There are no general purpose organs, hearts pump blood and livers detoxify the body. The same goes for psychological mechanisms; they arise as responses to specific contingencies in the environment and are selected for to the extent that they contribute to the survival and reproduction of the organism. Just as there are no general purpose organs, there are no general purpose psychological mechanisms. Finally, tenet 6 introduces the reductionist or foundational vision of evolutionary psychology, discussed above.

There are numerous examples of the kinds of mechanisms that are hypothesized to underlie our behavior on the basis of research guided by these theoretical tenets: the cheater-detection module; the mind-reading module; the waist/hip ratio detection module; the snake fear module and so on. A closer look at the waist/hip ratio detection module illustrates the above theoretical tenets at work. Devendra Singh (Singh 1993; Singh & Luis 1995) presents the waist/hip ratio detection module as one of the suite of modules that underlies mate selection in humans. This one is a specifically male psychological mechanism. Men detect variations in waist/hip ratio in women. Men’s preferences are for women with waist/hip ratios closer to .7. Singh claims that the detection and preference suite are adaptations for choosing fertile mates. So our mate selection behavior is explained in part by the underlying psychological mechanism for waist/hip ratio preference that was selected for in earlier human environments.

What is important to note about the research guided by these theoretical tenets above is that all behavior is best explained in terms of underlying psychological mechanisms that are adaptations for solving a particular set of problems that humans faced at one time in our ancestry. Also, evolutionary psychologists stress that the mechanisms they focus on are universally distributed in humans and are not susceptible to much, if any, variation. They maintain that the mechanisms are a product of adaptation but are no longer under selection (Tooby & Cosmides 2005, 39–40). Clark Barrett’s (2015) accessible and wide ranging introduction to evolutionary psychology sustains this emphasis on evolved mechanisms as the main focus of evolutionary psychology research. Barrett also expands the scope of evolutionary psychology and notes the addition of research methods developed since Cosmides and Tooby first set out the parameters for research in the field. Some of Barrett’s proposals are discussed in sections 6 and 7 below. Todd Shackleford and Viviana Weekes-Shackleford (2017) have just completed a huge compendium of work in the evolutionarily based psychological sciences. In this volume a vast array of different research methods are presented and defended and there are a number of entries comparing the merits of alternative approaches to evolutionary psychology.

The methods for testing hypotheses in evolutionary psychology come mostly from psychology. For example, in Singh’s work, male subjects are presented with drawings of women with varying waist hip ratios and ask to give their preference rankings. In Buss’s work supporting several hypothesized mate selection mechanisms, he performed similar experiments on subjects, asking for their responses to various questions about features of desired mates (Buss 1990). Buss, Singh and other evolutionary psychologists emphasize the cross cultural validity of their results, claiming consistency in responses across a wide variety of human populations. (But see Yu & Shepard 1998; Gray et al. 2003 for alternate conflicting results to Singh’s.) For the most part standard psychological experimental methods are used to test hypotheses in evolutionary psychology. This has raised questions about the extent to which the evolutionary component of evolutionary psychologists’ hypotheses is being tested (see, e.g., Shapiro & Epstein 1998; Lloyd 1999; Lloyd & Feldman 2002). A response profile may be prevalent in a wide variety of subject populations but this says nothing about whether or not the response profile is a psychological mechanism that arose from a particular selective regimen.

Claims that the mind has a modular architecture, and even massively modular architecture, are widespread in cognitive science (see, e.g., Hirshfield & Gelman 1994). The massive modularity thesis is first and foremost a thesis about cognitive architecture. As defended by evolutionary psychologists, the thesis is also about the source of our cognitive architecture: the massively modular architecture is the result of natural selection acting to produce each of the many modules (see, e.g., Barrett & Kurzban 2006; Barrett 2012). Our cognitive architecture is composed of computational devices, that are innate and are adaptations (Samuels 1998; Samuels et al. 1999a; Samuels et al. 1999b; Samuels 2000). This massively modular architecture accounts for all of our sophisticated behavior. Our successful navigation of the world results from the action of one or more of our many modules.

Jerry Fodor was the first to mount a sustained philosophical defense of modularity as a theory of cognitive architecture (Fodor 1983). His modularity thesis is distinct from the massive modularity thesis in a number of important ways. Fodor argued that our “input systems” are modular—for example, components of our visual system, our speech detection system and so on—these parts of our mind are dedicated information processors, whose internal make-up is inaccessible to other related processors. The modular detection systems feed output to a central system, which is a kind of inference engine. The central system, on Fodor’s view is not modular. Fodor presents a large number of arguments against the possibility of modular central systems. For example, he argues that central systems, to the extent that they engage in something like scientific confirmation, are “Quinean” in that “the degree of confirmation assigned to any given hypothesis is sensitive to properties of the entire belief system” (Fodor 1983, 107). Fodor draws a bleak conclusion about the status of cognitive science from his examination of the character of central systems: cognitive science is impossible. So on Fodor’s view, the mind is partly modular and the part of the mind that is modular provides some subject matter for cognitive science.

A distinct thesis from Fodor’s, the massive modularity thesis, gets a sustained philosophical defense from Peter Carruthers (see especially Carruthers 2006). Carruthers is well aware that Fodor (see e.g. Fodor 2000) does not believe that central systems can be modular but he presents arguments from evolutionary psychologists and others that support the modularity thesis for the whole mind. Perhaps one of the reasons that there is so much philosophical interest in evolutionary psychology is that discussions about the status of the massive modularity thesis are highly theoretical. [ 3 ] Both evolutionary psychologists and philosophers present and consider arguments for and against the thesis rather than simply waiting until the empirical results come in. Richard Samuels (1998) speculates that argument rather than empirical data is relied on, because the various competing modularity theses about central systems are hard to pull apart empirically. Carruthers exemplifies this approach as he relies heavily on arguments for massive modularity often at the expense of specific empirical results that tell in favor of the thesis.

There are many arguments for the massive modularity thesis. Some are based upon considerations about how evolution must have acted; some are based on considerations about the nature of computation and some are versions of the poverty of the stimulus argument first presented by Chomsky in support of the existence of an innate universal grammar. (See Cowie 1999 for a nice presentation of the structure of poverty of the stimulus arguments.) Myriad versions of each of these arguments appear in the literature and many arguments for massive modularity mix and match components of each of the main strands of argumentation. Here we review a version of each type of argument.

Carruthers presents a clear outline of the first type of argument “the biological argument for massive modularity”: “(1) Biological systems are designed systems, constructed incrementally. (2) Such systems, when complex, need to have massively modular organization. (3) The human mind is a biological system and is complex. (4) So the human mind will be massively modularly in its organization” (Carruthers 2006, 25). An example of this argument is to appeal to the functional decomposition of organisms into organs “designed” for specific tasks, e.g. hearts, livers, kidneys. Each of these organs arises as a result of natural selection and the organs, acting together, contribute to the fitness of the organism. The functional decomposition is driven by the response to specific environmental stimuli. Rather than natural selection acting to produce general purpose organs, each specific environmental challenge is dealt with by a separate mechanism. All versions of this argument are arguments from analogy, relying on the key transitional premise that minds are a kind of biological system upon which natural selection acts.

The second type of argument makes no appeal to biological considerations whatsoever (although many evolutionary psychologists give these arguments a biological twist). Call this the computational argument, which unfolds as follows: minds are computational problem solving devices; there are specific types of solutions to specific types of problems; and so for minds to be (successful) general problem solving devices, they must consist of collections of specific problem solving devices, i.e. many computational modules. This type of argument is structurally similar to the biological argument (as Carruthers points out). The key idea is that there is no sense to the idea of a general problem solver and that no headway can be made in cognitive science without breaking down problems into their component parts.

The third type of argument involves a generalization of Chomsky’s poverty of the stimulus argument for universal grammar. Many evolutionary psychologists (see, e.g., Tooby & Cosmides 1992) appeal to the idea that there is neither enough time, nor enough available information, for any given human to learn from scratch to successfully solve all of the problems that we face in the world. This first consideration supports the conclusion that the underlying mechanisms we use to solve the relevant problems are innate (for evolutionary psychologists “innate” is usually interchangeable with “product of natural selection” [ 4 ] ). If we invoke this argument across the whole range of problem sets that humans face and solve, we arrive at a huge set of innate mechanisms that subserve our problem solving abilities, which is another way of saying that we have a massively modular mind.

There are numerous responses to the many versions of each of these types of arguments and many take on the massive modularity thesis head on without considering a specific argument for it. I will defer consideration of responses to the first argument type until section 4 below, which focuses on issues of the nature of evolution and natural selection – topics in philosophy of biology.

The second type of argument is one side of a perennial debate in the philosophy of cognitive science. Fodor (2000, 68) takes this argument to rest on the unwarranted assumption that there is no domain-independent criterion of cognitive success, which he thinks requires an argument that evolutionary psychologists do not provide. Samuels (see esp. Samuels 1998) responds to evolutionary psychologists that arguments of this type do not sufficiently discriminate between a conclusion about domain specific processing mechanisms and domain specific knowledge or information. Samuels articulates what he calls the “library model of cognition” in which there is domain specific information or knowledge but domain general processing. The library model of cognition is not massively modular in the relevant sense but type two arguments support it. According to Samuels, evolutionary psychologists need something more than this type of argument to warrant their specific kind of conclusion about massive modularity. Buller (2005) introduces further worries for this type of argument by tackling the assumption that there can be no such thing as a domain general problem solving mechanism. Buller worries that in their attempt to support this claim, evolutionary psychologists fail to adequately characterize a domain general problem solver. For example, they fail to distinguish between a domain general problem solver and a domain specific problem solver that is over generalized. He offers the example of social learning as a domain general mechanism that would produce domain specific solutions to problems. He uses a nice biological analogy to drive this point home: the immune system is a domain general system in that it allows the body to respond to a wide variety of pathogens. While it is true that the immune system produces domain specific responses to pathogens in the form of specific antibodies, the antibodies are produced by one domain general system. These and many other respondents conclude that type two arguments do not adequately support the massive modularity thesis.

Fodor (2000) and Kim Sterelny (2003) provide different responses to type three arguments. Fodor’s response is that poverty of the stimulus type arguments support conclusions about innateness but not modularity and so these arguments can not be used to support the massive modularity thesis. He argues that the domain specificity and encapsulation of a mechanism and its innateness pull apart quite clearly, allowing for “perfectly general learning mechanisms” that are innate and “fully encapsulated mechanisms” that are single stimulus specific and everything in between. Sterelny responds to the generalizing move in type three arguments. He takes language to be the exception rather than the rule in the sense that while the postulation of an innate, domain specific module may be warranted to account for our language abilities, much of our other problem solving behavior can be accounted for without postulating such modules (Sterelny 2003, 200). [ 5 ] Sterelny’s counter requires invoking alternate explanations for our behavioral repertoire. For example, he accounts for folk psychology and folk biology by appealing to environmental factors, some of which are constructed by our forebears, that allow us to perform sophisticated cognitive tasks. If we can account for our success at various complex problem solving tasks, without appealing to modules, then the massive modularity thesis is undercut. Sterelny sharpens his response to massive modularity by adding more detail to his accounts of how many of our uniquely human traits may have evolved (see, e.g., Sterelny 2012). Sterelny introduces his “evolved apprentice” model to account for the evolution of many human traits that many assume require explanation in terms of massive modularity, for example, forming moral judgments. Cecilia Heyes adopts a similar approach to Sterenly in attacking massive modularity. Rather than presenting arguments against massive modularity, she offers alternative explanations of the development of folk psychology that do not rely on the massive modularity thesis (Heyes 2014a; Heyes 2014b).

Heyes and Sterelny not only reject massive modularity but also have little expectation that any modularity theses will bear fruit but there are many critics of the massive modularity thesis who allow for the possibility of some modularity of mind. Such critics of evolutionary psychology do not reject the possibility of any kind of modularity, they just reject the massive modularity thesis. There is considerable debate about the status of the massive modularity thesis and some of this debate centers around the characterization of modules. If modules have all the characteristics that Fodor (1983) first presented, then he may be right that central systems are not modular. Both Carruthers (2006) and Barrett and Kurzban (2006) present modified characterizations of modules, which they argue better serve the massive modularity thesis. There is no agreement on a workable characterization of modules for evolutionary psychology but there is agreement on the somewhat benign thesis that “the language of modularity affords useful conceptual groundwork in which productive debates surrounding cognitive systems can be framed” (Barrett and Kurzban 2006, 644).

Many philosophers have criticized evolutionary psychology. Most of these critics are philosophers of biology who argue that the research tradition suffers from an overly zealous form of adaptationism (Griffiths 1996; Richardson 1996; Grantham & Nichols 1999; Lloyd 1999; Richardson 2007), an untenable reductionism (Dupré 1999, 2001), a “bad empirical bet” about modules (Sterelny 1995; Sterelny & Griffiths 1999; Sterelny 2003), a fast and loose conception of fitness (Lloyd 1999; Lloyd & Feldman 2002); and most of the above and much more (Buller 2005). (See also Downes 2005.) [ 6 ] All of these philosophers share one version or other of Buller’s view: “I am unabashedly enthusiastic about efforts to apply evolutionary theory to human psychology” (2005, x). [ 7 ] But if philosophers of biology are not skeptical of the fundamental idea behind the project, as Buller’s quote indicates, what are they so critical of? What is at stake are differing views about how to best characterize evolution and hence how to generate evolutionary hypotheses and how to test evolutionary hypotheses. For evolutionary psychologists, the most interesting contribution that evolutionary theory makes is the explanation of apparent design in nature or the explanation of the production of complex organs by appeal to natural selection. Evolutionary psychologists generate evolutionary hypotheses by first finding apparent design in the world, say in our psychological make up, and then presenting a selective scenario that would have led to the production of the trait that exhibits apparent design. The hypotheses evolutionary psychologists generate, given that they are usually hypotheses about our psychological capacities, are tested by standard psychological methods. Philosophers of biology challenge evolutionary psychologists on both of these points. I introduce a few examples of criticisms in each of these two areas below and then look at some responses to philosophical criticisms of evolutionary psychology.

Adaptation is the one biological concept that is central to most debates over evolutionary psychology. Every theoretical work on evolutionary psychology presents the research tradition as being primarily focused on psychological adaptations and goes on to give an account of what adaptations are (see, e.g., Tooby & Cosmides 1992; Buss et al. 1998; Simpson & Campbell 2005; Tooby & Cosmides 2005). Much of the philosophical criticism of evolutionary psychology addresses its approach to adaptation or its form of adaptationism. Let us quickly review the basics from the perspective of philosophy of biology.

Here is how Elliott Sober defines an adaptation: “characteristic c is an adaptation for doing task t in a population if and only if members of the population now have c because, ancestrally, there was selection for having c and c conferred a fitness advantage because it performed task t ” (Sober 2000, 85). Sober makes a few further clarifications of the notion of adaptation that are helpful. First, we should distinguish between a trait that is adaptive and a trait that is an adaptation . Any number of traits can be adaptive without those traits being adaptations. A sea turtle’s forelegs are useful for digging in the sand to bury eggs but they are not adaptations for nest building (Sober 2000, 85). Also, traits can be adaptations without being currently adaptive for a given organism. Vestigial organs such as our appendix or vestigial eyes in cave dwelling organisms are examples of such traits (Sterelny and Griffiths 1999). Second, we should distinguish between ontogenic and phylogenetic adaptations (Sober 2000, 86). The adaptations of interest to evolutionary biologists are phylogenetic adaptations, which arise over evolutionary time and impact the fitness of the organism. Ontogenetic adaptations, including any behavior we learn in our lifetimes, can be adaptive to the extent that an organism benefits from them but they are not adaptations in the relevant sense. Finally, adaptation and function are closely related terms. On one of the prominent views of function—the etiological view of functions—adaptation and function are more or less coextensive; to ask for the function of an organ is to ask why it is present. On the Cummins view of functions adaptation and function are not coextensive, as on the Cummins view, to ask what an organ’s function is, is to ask what it does (Sober 2000, 86–87). (See also Sterelny & Griffiths 1999, 220–224.)

Evolutionary psychologists focus on psychological adaptations. One consistent theme in the theoretical work of evolutionary psychologists is that “adaptations, the functional components of organisms, are identified […] by […] evidence of their design: the exquisite match between organism structure and environment” (Hagen 2005, 148). The way in which psychological adaptations are identified is by evolutionary functional analysis, which is a type of reverse engineering. [ 8 ] “Reverse engineering is a process of figuring out the design of a mechanism on the basis of an analysis of the tasks it performs. Evolutionary functional analysis is a form of reverse engineering in that it attempts to reconstruct the mind’s design from an analysis of the problems the mind must have evolved to solve” (Buller 2005, 92). Many philosophers object to evolutionary psychologists’ over attribution of adaptations on the basis of apparent design. Here some are following Gould and Lewontin’s (1979) lead when they worry that accounting for apparent design in nature in terms of adaptation amounts to telling just-so stories but they could just as easily cite Williams (1966), who also cautioned against the over attribution of adaptation as an explanation for biological traits. While it is true that evolutionary functional analysis can lend itself to just-so story telling, this is not the most interesting problem that confronts evolutionary psychology, several other interesting problems have been identified. For example, Elisabeth Lloyd (1999) derives a criticism of evolutionary psychology from Gould and Lewontin’s criticism of sociobiology, emphasizing the point that evolutionary psychologists’ adaptationism leads them to ignore alternative evolutionary processes. Buller takes yet another approach to evolutionary psychologists’ adaptationism. What lies behind Buller’s criticisms of evolutionary psychologists’ adaptationism is a different view than theirs about what is important in evolutionary thinking (Buller 2005). Buller thinks that evolutionary psychologists overemphasize design and that they make the contentious assumption that with respect to the traits they are interested in, evolution is finished, rather than ongoing.

Sober’s definition of adaptation is not constrained only to apply to organs or other traits that exhibit apparent design. Rather, clutch size (in birds), schooling (in fish), leaf arrangement, foraging strategies and all manner of traits can be adaptations (Seger & Stubblefield 1996). Buller argues the more general point that phenotypic plasticity of various types can be an adaptation, because it arises in various organisms as a result of natural selection. [ 9 ] The difference here between Buller (and other philosophers and biologists) and evolutionary psychologists is a difference in the explanatory scope that they attribute to natural selection. For evolutionary psychologists, the hallmark of natural selection is a well functioning organ and for their critics, the results of natural selection can be seen in an enormous range of traits ranging from the specific apparent design features of organs to the most general response profiles in behavior. According to Buller, this latter approach opens up the range of possible evolutionary hypotheses that can account for human behavior. Rather than being restricted to accounting for our behavior in terms of the joint output of many specific modular mechanisms, we can account for our behavior by appealing to selection acting upon many different levels of traits. This difference in emphasis on what is important in evolutionary theory also is at the center of debates between evolutionary psychologists and behavioral ecologists, who argue that behaviors, rather than just the mechanisms that underlie them, can be adaptations (Downes 2001). Further, this difference in emphasis is what leads to the wide range of alternate evolutionary hypotheses that Sterelny (Sterelny 2003) presents to explain human behavior. Given that philosophers like Buller and Sterelny are adaptationists, they are not critical of evolutionary psychologists’ adaptationism. Rather, they are critical of the narrow explanatory scope of the type of adaptationism evolutionary psychologists adopt (see also Downes 2015).

Buller’s criticism that evolutionary psychologists assume that evolution is finished for the traits that they are interested in connects worries about the understanding of evolutionary theory with worries about the testing of evolutionary hypotheses. Here is Tooby & Cosmides’ clear statement of the assumption that Buller is worried about: “evolutionary psychologists primarily explore the design of the universal, evolved psychological and neural architecture that we all share by virtue of being human. Evolutionary psychologists are usually less interested in human characteristics that vary due to genetic differences because they recognize that these differences are unlikely to be evolved adaptations central to human nature. Of the three kinds of characteristics that are found in the design of organisms – adaptations, by-products, and noise – traits caused by genetic variants are predominantly evolutionary noise, with little adaptive significance, while complex adaptations are likely to be universal in the species” (Tooby & Cosmides 2005, 39). This line of thinking also captures evolutionary psychologists’ view of human nature: human nature is our collection of universally shared adaptations. (See Downes & Machery 2013 for more discussion of this and other, contrasting biologically based accounts of human nature.) The problem here is that it is false to assume that adaptations cannot be subject to variation. The underlying problem is the constrained notion of adaptation. Adaptations are traits that arise as a result of natural selection and not traits that exhibit design and are universal in a given species (Seger & Stubblefield 1996). As a result, it is quite consistent to argue, as Buller does, that many human traits may still be under selection and yet reasonably be called adaptations. Finally, philosophers of biology have articulated several different types of adaptationism (see, e.g., Godfrey-Smith 2001; Lewens 2009; Sober 2000). While some of these types of adaptationism can be reasonably seen placing constraints on how evolutionary research is carried out, Godfrey-Smith’s “explanatory adaptationism” is different in character (Godfrey-Smith 2001). Explanatory adaptationism is the view that apparent design is one of the big questions we face in explaining our natural world and natural selection is the big (and only supportable) answer to such a big question. Explanatory adaptationism is often adopted by those who want to distinguish evolutionary thinking from creationism or intelligent design and is the way evolutionary psychologists often couch their work to distinguish it from their colleagues in the broader social sciences. While explanatory adaptationism does serve to distinguish evolutionary psychology from such markedly different approaches to accounting for design in nature, it does not place many clear constraints on the way in which evolutionary explanations should be sought (Downes 2015). So far these are disagreements that are located in differing views about the nature and scope of evolutionary explanation but they have ramifications in the discussion about hypothesis testing.

If the traits of interest to evolutionary psychologists are universally distributed, then we should expect to find them in all humans. This partly explains the stock that evolutionary psychologists put in cross cultural psychological tests (see, e.g., Buss 1990). If we find evidence for the trait in a huge cross section of humans, then this supports our view that the trait is an adaptation —on the assumption that adaptations are organ-like traits that are products of natural selection but not subject to variation. But given the wider scope view of evolution defended by philosophers of biology, this method of testing seems wrong-headed as a test of an evolutionary hypothesis. Certainly such testing can result in the very interesting results that certain preference profiles are widely shared cross culturally but the test does not speak to the evolutionary hypothesis that the preferences are adaptations (Lloyd 1999; Buller 2005).

Another worry that critics have about evolutionary psychologists’ approach to hypothesis testing is that they give insufficient weight to serious alternate hypotheses that fit the relevant data. Buller dedicates several chapters of his book on evolutionary psychology to an examination of hypothesis testing and many of his criticisms center around the introduction of alternate hypotheses that do as good a job, or a better job, of accounting for the data. For example, he argues that the hypothesis of assortative mating by status does a better job of accounting for some of evolutionary psychologists’ mate selection data than their preferred high status preference hypothesis. This debate hangs on how the empirical tests come out. The previous debate is more closely connected to theoretical issues in philosophy of biology.

I said in my introduction that there is a broad consensus among philosophers of science that evolutionary psychology is a deeply flawed enterprise and some philosophers of biology continue to remind us of this sentiment (see, e.g., Dupré 2012). However the relevant consensus is not complete, there are some proponents of evolutionary psychology among philosophers of science. One way of defending evolutionary psychology is to rebut criticism. Edouard Machery and Clark Barrett (2007) do just that in their sharply critical review of Buller’s book. Another way to defend evolutionary psychology is to practice it (at least to the extent that philosophers can, i.e. theoretically). This is what Robert Arp (2006) does in a recent article. I briefly review both responses below.

Machery and Barrett (2007) argue that Buller has no clear critical target as there is nothing to the idea that there is a research tradition of evolutionary psychology that is distinct from the broader enterprise of the evolutionary understanding of human behavior. They argue that theoretical tenets and methods are shared by many in the biology of human behavior. For example, many are adaptationists. But as we saw above, evolutionary psychologists and behavioral ecologists can both call themselves adaptationist but their particular approach to adaptationism dictates the range of hypotheses that they can generate, the range of traits that can be counted as adaptations and impacts upon the way in which hypotheses are tested. Research traditions can share some broad theoretical commitments and yet still be distinct research traditions. Secondly, they argue against Buller’s view that past environments are not stable enough to produce the kind of psychological adaptations that evolutionary psychologists propose. They take this to be a claim that no adaptations can arise from an evolutionary arms race situation, for example, between predators and prey. But again, I think that the disagreement here is over what counts as an adaptation. Buller does not deny that adaptations— traits that arise as a product of natural selection—arise from all kinds of unstable environments. What he denies is that organ-like, special purpose adaptations are the likely result of such evolutionary scenarios.

Arp (2006) defends a hypothesis about a kind of module—scenario visualization—a psychological adaptation that arose in our hominid history in response to the demands of tool making, such as constructing spear throwing devices for hunting. Arp presents his hypothesis in the context of demonstrating the superiority of his approach to evolutionary psychology, which he calls “Narrow Evolutionary Psychology,” over “Broad Evolutionary Psychology,” with respect to accounting for archaeological evidence and facts about our psychology. While Arp’s hypothesis is innovative and interesting, he by no means defends it conclusively. This is partly because his strategy is to compare his hypothesis with archaeologist Steven Mithen’s (1996) non-modular “cognitive fluidity” hypothesis that is proposed to account for the same data. The problem here is that Mithen’s view is only one of the many alternative, evolutionary explanations of human tool making behavior. While Arp’s modular thesis may be superior to Mithen’s, he has not compared it to Sterelny’s (2003; 2012) account of tool making and tool use or to Boyd and Richerson’s (see, e.g., 2005) account and hence not ruled these accounts out as plausible alternatives. As neither of these alternative accounts rely on the postulation of psychological modules, evolutionary psychology is not adequately defended.

Many philosophers who work on moral psychology understand that their topic is empirically constrained. Philosophers take two main approaches to using empirical results in moral psychology. One is to use empirical results (and empirically based theories from psychology) to criticize philosophical accounts of moral psychology (see, e.g., Doris 2002) and one is to generate (and, in the experimental philosophy tradition, to test) hypotheses about our moral psychology (see, e.g., Nichols 2004). For those who think that some (or all) of our moral psychology is based in innate capacities, evolutionary psychology is a good source of empirical results and empirically based theory. One account of the make-up of our moral psychology follows from the massive modularity account of the architecture of the mind. Our moral judgments are a product of domain specific psychological modules that are adaptations and arose in our hominid forebears in response to contingencies in our (mostly) social environments. This position is currently widely discussed by philosophers working in moral psychology. An example of this discussion follows.

Cosmides (see, e.g., 1989) defends a hypothesis in evolutionary psychology that we have a cheater-detection module. [ 10 ] This module is hypothesized to underlie important components of our behavior in moral domains and fits with the massively modular view of our psychology in general. Cosmides (along with Tooby) argues that cheating is a violation of a particular kind of conditional rule that goes along with a social contract. Social exchange is a system of cooperation for mutual benefit and cheaters violate the social contract that governs social exchange (Cosmides & Tooby 2005). The selection pressure for a dedicated cheater-detection module is the presence of cheaters in the social world. The cheater-detection module is an adaptation that arose in response to cheaters. The cheater-detection hypothesis has been the focus of a huge amount of critical discussion. Cosmides and Tooby (2008) defend the idea that cheat detection is modular over hypotheses that more general rules of inference are involved in the kind of reasoning behind cheater detection against critics Ron Mallon (2008) and Fodor (2008). Some criticism of the cheater-detection hypothesis involves rehashing criticisms of massive modularity in general and some treats the hypothesis as a contribution to moral psychology and invokes different considerations. For example, Mallon (2008) worries about the coherence of abandoning a domain general conception of ought in our conception of our moral psychology. This discussion is also ongoing. (See, e.g., Sterelny 2012 for a selection of alternate, non-modular explanations of aspects of our moral psychology.)

Evolutionary psychology is well suited to providing an account of human nature. As noted above (Section 1), evolutionary psychology owes a theoretical debt to human sociobiology. E.O. Wilson took human sociobiology to provide us with an account of human nature (1978). For Wilson human nature is the collection of universal human behavioral repertoires and these behavioral repertoires are best understood as being products of natural selection. Evolutionary psychologists argue that human nature is not a collection of universal human behavioral repertoires but rather the universal psychological mechanisms underlying these behaviors (Tooby & Cosmides 1990). These universal psychological mechanisms are products of natural selection, as we saw in Section 2. above. Tooby and Cosmides put this claim as follows: “the concept of human nature is based on a species-typical collection of complex psychological adaptations” (1990, 17). So, for evolutionary psychologists, “human nature consists of a set of psychological adaptations that are presumed to be universal among, and unique to, human beings” (Buller 2005, 423). Machery’s (2008) nomological account of human nature is based on, and very similar to, the evolutionary psychologists’ account. Machery says that “human nature is the set of properties that humans tend to possess as a result of the evolution of their species” (2008, 323). While Machery’s account appeals to traits that have evolved and are universal (common to all humans), it is not limited to psychological mechanisms. For example, he thinks of bi-pedalism as part of the human nature trait cluster. Machery’s view captures elements of both the sociobiological view and the evolutionary psychology view of human nature. He shares the idea that a trait must be a product of evolution, rather than say social learning or enculturation, with both these accounts.

Some critical challenges to evolutionary psychological accounts of human nature (and the nomological account) derive from similar concerns as those driving criticism of evolutionary psychology in general. In Section 4. we see that discussions of evolutionary psychology are founded on disagreements about how adaptation should be characterized and disagreements about the role of variation in evolution. Some critics charge evolutionary psychologists of assuming that adaptation cannot sustain variation. Buller’s (2005) criticism of evolutionary psychologists’ account of human nature also invokes variation (Here he follows Hull 1986 and Sober 1980). The idea here is that humans, like all organisms, exhibit a great deal of variation, including morphological, physiological, behavioral and cultural variation (see also Amundson 2000). Buller argues that the evolutionary psychology account of human nature either ignores or fails to account for all of this variation (see also Lewens 2015 and Ramsey 2013). Any account that restricts human nature to just those traits we have in common and which also are not subject to change, cannot account for human variation.

Buller’s (2005) criticism of evolutionary psychologists’ notion of human nature (or the nomological account) is based on the idea that we vary across many dimensions and an account of human nature based on fixed, universal traits cannot account for any of this variation. The idea that to account for human nature, we must account for human variation is presented and defended by evolutionary psychologists (see, e.g., Barrett 2015), anthropologists (see e.g. Cashdan 2013) and philosophers (see, e.g., Griffiths 2011 and Ramsey 2013). Barrett agrees with Buller (and others) that evolutionary psychologists have failed to account for human variation in their account of human nature. Rather than seeing this challenge as a knock down of the whole enterprise of accounting for human nature, Barrett sees this as a challenge for an account of human nature. Barrett says “Whatever human nature is, it’s a biological phenomenon with all that implies” (2015, 321). So, human nature is “a big wobbly cloud that is different from the population clouds of squirrels and palm trees. To understand human minds and behaviors, we need to understand the properties of our own cloud, as messy as it might be” (2015, 232). Rather than human nature being a collection of shared fixed universal psychological traits, for Barrett, human nature is the whole human trait cluster, including all of the variation in all of our traits. This approach to human nature is sharply different than the approach defended by either Wilson, Tooby and Cosmides or Machery but is also subject to a number of criticisms. The main thrust of the criticisms is that such a view cannot be explanatory and is instead merely a big list of all the properties that humans have had and can have (see, e.g., Buller 2005; Downes 2016; Futuyma 1998; and Lewens 2015). Discussion over the tension between evolutionary psychologists’ views and the manifest variation in human traits continues in many areas that evolutionary psychologists focus on. Another example of this broader discussion is included in Section 7. below.

Evolutionary psychology is invoked in a wide range of areas of study, for example, in English Literature, Consumer Studies and Law. (See Buss 2005 for discussion of Literature and Law and Saad 2007 for a detailed presentation of evolutionary psychology and consumer studies.) In these contexts, evolutionary psychology is usually introduced as providing resources for practitioners, which will advance the relevant field. Philosophers have responded critically to some of these applications of evolutionary psychology. One concern is that often evolutionary psychology is conflated with evolution or evolutionary theory in general (see, e.g., Leiter & Weisberg 2009 and Downes 2013). The discussion reviewed in Section 4. above, reveals a good deal of disagreement between evolutionary theorists and evolutionary psychologists over the proper account of evolution. Evolutionary psychologists offer to enhance fields such as Law and Consumer Studies by introducing evolutionary ideas but what is in fact offered is a selection of theoretical resources championed only by proponents of a specific approach to evolutionary psychology. For example, Gad Saad (2007) argues that Consumer Studies will profit greatly from the addition of adaptive thinking, i.e. looking for apparent design, and by introducing hypothetical evolved modules to account for consumer behavior. However, this does not appear to be an effort to bring evolutionary theory, broadly construed, to bear on Consumer Studies (Downes 2013). Promoting disputed theoretical ideas is certainly problematic but bigger worries arise when thoroughly discredited work is promoted in the effort to apply evolutionary psychology. Owen Jones (see, e.g., 2000; 2005), who believes that Law will benefit from the application of evolutionary psychology, champions Randy Thornhill and Craig Palmer’s (2000) widely discredited view that rape is an adaptation as exemplary evolutionary work (see de Waal 2000, Coyne & Berry 2000, Coyne 2003, Lloyd 2003, Vickers & Kitcher 2003, and Kimmel 2003). Further, Jones (2000) claims that the critics of Thornhill and Palmer’s work have no credibility as scientists and evolutionary theorists. This claim indicates Jones’ serious disconnect with the wider scientific (and philosophical) literature on evolutionary theory (Leiter & Weisberg 2009).

Aside from monitoring the expansion efforts of evolutionary psychology, there are a number of other areas in which further philosophical work on evolutionary psychology will be fruitful. The examples given above of work in moral psychology barely scratch the surface of this rapidly developing field. There are huge numbers of empirical hypotheses that bear on our conception of our moral psychology that demand philosophical scrutiny. (Hauser 2006 includes a survey of a wide range of such hypotheses.) Also, work on moral psychology and the emotions can be drawn together via work on evolutionary psychology and related fields. Griffiths (1997) directed philosophical attention to evolution and the emotions and this kind of work has been brought into closer contact with moral psychology by Nichols (see, e.g., his 2004). In philosophy of mind there is still much that can be done on the topic of modules. Work on integrating biological and psychological concepts of modules is one avenue that is being pursued and could be fruitfully pursued further (see, e.g., Barrett & Kurzban 2006; Carruthers 2006) and work on connecting biology to psychology via genetics is another promising area (see e.g. Marcus 2004). In philosophy of science, I have no doubt that many more criticisms of evolutionary psychology will be presented but a relatively underdeveloped area of philosophical research is on the relations among all of the various, theoretically different, approaches to the biology of human behavior (but see Downes 2005; Griffiths 2008; and Brown et al. 2011). Evolutionary psychologists present their work alongside the work of behavioral ecologists, developmental psychobiologists and others (see, e.g., Buss 2005; Buss 2007) but do not adequately confront the theoretical difficulties that face an integrated enterprise in the biology of human behavior. Finally, while debate rages between biologically influenced and other social scientists, most philosophers have not paid much attention to potential integration of evolutionary psychology into the broader interdisciplinary study of society and culture (but see Mallon and Stich 2000 on evolutionary psychology and constructivism). In contrast, feminist philosophers have paid attention to this integration issue as well as offered feminist critiques of evolutionary psychology (see Fehr 2012, Meynell 2012 and the entry on feminist philosophy of biology ). Gillian Barker (2015), shares some evolutionarily based criticisms of evolutionary psychology with philosophers of biology discussed in Section 4. but also assesses evolutionary psychology in relation to other social sciences. She also adds a novel critical appraisal of evolutionary psychology. She argues that, as currently practiced, evolutionary psychology is not a fruitful guide to social policy regarding human flourishing.

The publication of Shackleford and Weekes-Shackleford’s (2017) huge collection of articles on issues arising in the evolutionary psychological sciences provides a great resource for philosophers looking for material to fuel critical discussion. Many evolutionary psychologists are aware of the difficulty variation presents for some established approaches in their field. This issue confronts those interested in developing accounts of human nature, as noted above (Section 6.), but also arises when confronting many of the varying human behaviors evolutionary psychologists seek to account for. For example, human aggression varies along many dimensions and confronting and accounting for each of these types of variation is a challenge for many evolutionary psychologists (Downes & Tabery 2017). Given that evolutionary psychology is just one, among many, evolutionarily based approaches to explaining human behavior, the most promising critical discussions of evolutionary psychology should continue to come from work that compares hypotheses drawn from evolutionary psychology with hypotheses drawn from other evolutionary approaches and other approaches in the social sciences more broadly construed. Stephan Linquist (2016) takes this approach to evolutionary psychologists’ work on cultures of honor. Linquist introduces hypotheses from cultural evolution that appear to offer more explanatory bite than those from evolutionary psychology. The broader issue of tension between evolutionary psychology and cultural evolution here will doubtless continue to attract the critical attention of philosophers. (See Lewens 2015 for a nice clear introduction to and discussion of alternative approaches to cultural evolution.)

Interest has re-emerged in the relation(s) between evolutionary psychology and the other social sciences (Buss 2020). Some time ago, John Dupré (1994) diagnosed evolutionary psychology as an exercise in scientific imperialism. Dupré later characterized scientific imperialism as “the tendency for a successful scientific idea to be applied far beyond its original home, and generally with decreasing success the more its application is expanded” (2001, 16). Dupré uses “scientific imperialism” in a pejorative sense and marshals this as a criticism of evolutionary psychology. (See Downes 2017 for further discussion of scientific imperialism and evolutionary psychology.) Buss (2020) does not cite Dupré but might well be responding to him when he proposes that evolutionary psychology constitutes a scientific revolution in Kuhn’s sense. Buss argues that evolutionary psychology is superior to other approaches in psychology, because it has supplanted them (or at least should supplant them) just as Einstein’s physics supplanted Newton’s or just as cognitive psychology supplanted behaviorism. (David Reich [2018] casts ancient DNA research in similarly Kuhnian terms and offers it up as superior to all previous approaches in archaeology.) Buss takes evolutionary psychology to be a meta-theoretical approach best fit for guiding all of psychology. This is one of the many ways in which his appeal to Kuhn is strained, as Buss is not looking back on the supplanting of one theoretical framework by another but rather arguing for the superiority of his approach to others available in psychology. A further, and quite specific way that Buss sees evolutionary psychology as superior to other approaches in psychology (and the social sciences in general, is that evolutionary psychology ignores (or should ignore) proximate explanations. For Buss, evolutionary psychology offers ultimate explanations and these are enough. However, many areas of biology, for example, physiology, trade in proximate explanations and are not likely to be cast aside because of this focus. This implies that there is still a place for proximate explanations in psychology. This brief discussion indicates that the relations between evolutionary psychology and the rest of psychology, and the social sciences, more broadly is a topic well worth pursuing by philosophers of science and Buss’ and Dupré’s accounts present interesting alternate starting points in this endeavor.

Finally, philosophers of science will doubtless continue to check the credentials of evolutionary ideas imported into other areas of philosophy. Philosophers of biology in particular, still voice suspicion if philosophers borrow their evolutionary ideas from evolutionary psychology rather than evolutionary biology. Philip Kitcher (2017) voices this concern with regards to Sharon Street’s (2006) appeals to evolution. Kitcher worries that Street does not rely on “what is known about human evolution” (2017, 187) to provide an account of how her traits of interest may have emerged. As noted above, Machery’s nomological notion of human nature (2008; 2017) is criticized on the grounds that he takes his idea of an evolved trait from evolutionary psychology as opposed to evolutionary biology. Barker (2015) also encourages philosophers, as well as social scientists, to draw from the huge range of theoretical resources evolutionary biologists have to offer, rather than just from those provided by evolutionary psychologists.

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Cited Resources

  • Buller, D., 2000, “ Evolutionary Psychology ” (a guided tour), in M. Nani and M. Marraffa (eds.), A Field Guide to the Philosophy of Mind .

adaptationism | biology: philosophy of | cognitive science | culture: and cognitive science | emotion | feminist philosophy, interventions: philosophy of biology | -->function --> | game theory: evolutionary | innate/acquired distinction | innateness: and language | language of thought hypothesis | mind: modularity of | moral psychology: empirical approaches | prisoner’s dilemma

Acknowledgments

Thanks to Austin Booth, David Buller, Marc Ereshefsky, Matt Haber, Ron Mallon, Shaun Nichols and the Stanford Encyclopedia referees for helpful comments on drafts of this entry.

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10 Evolutionary Psychology Examples

evolutionary psychology examples and definition

Evolutionary psychology aims to understand how thoughts, actions, and behavior are shaped by evolutionary forces (Mealey, 2023; Workman, 2004).

Evolutionary psychology proposes that the human brain and mind have developed in ways that were evolutionarily advantageous to our ancestors.

Therefore, according to this approach, we need to understand the evolutionary origins of mental processes to fully understand human behavior.

The mental processes and mechanisms that have evolved to solve problems of survival and reproduction are called psychological adaptations.  

An example of evolutionary psychology is the investigation of the underlying psychological reasons we might prefer to mate with partners with certain physical or behavioral traits.

Evolutionary Psychology Definition and Explanation

Evolutionary psychology has its roots in Darwin’s theory of natural selection.

Charles Darwin observed groups of finches on various islands. He noticed that the birds seemed to have developed physical and behavioral changes that better suited them for survival on their respective islands.

Darwin took his observations and developed the theory of natural selection . He proposed that certain traits become common in a population based on how well those traits help the organisms in a species survive and reproduce.

The traits that help organisms survive and reproduce are passed down from parent to offspring. Eventually, this process can lead to the development of new species. This long-term change in the characteristics of a species over many generations is evolution .     

Like every other species on the planet, humans have evolved over time.

In the example of birds above, those adaptive traits included beak size. However, evolutionary psychology aims to apply the principles of natural selection to understand why modern humans think and behave the way we do.       

Evolutionary psychology is set apart from other psychological disciplines because it typically explains human behavior through the lens of survival and reproduction.

Theories in Evolutionary Psychology

Two popular theories in evolutionary psychology include the sexual strategies theory and error management theory.

1. Sexual Strategies Theory

Sexual strategies theory proposes that humans have evolved different long and short-term mating strategies that may depend on many factors like culture and social context.

This theory focuses on similarities and differences in men’s and women’s mating preferences and strategies.

The theory proposes that women have inherited the trait of desiring mates who possess resources. In contrast, men have inherited the trait of desiring health.

Many factors, beyond resources or health, like culture, context, and personality, will influence who people choose to be their partners (Buss, 2023).

2. Error Management Theory

Error management theory (EMT) explains how we think, make decisions, and evaluate uncertain or novel situations.

We must make decisions constantly; some errors are more costly than others. EMT explains that we have evolved to make decisions that will result in less costly errors (Buss, 2023).

  • Explaining Perception in Infants . Some essential aspects of human behavior seem to be innate even early on. Cognitive functions, like perceiving a steep drop off or an object coming towards you, are present in infants. For example, infants are weary of steep drop-offs, even if they haven’t experienced a fall (Mealey, 2023).    
  • Explaining Mate Selection through Evolution . Much of evolutionary psychology is concerned with relationships since they are important to understanding reproduction. Some evolutionary psychology tries to explain why people prefer specific characteristics in other people – like facial symmetry.   
  • Explaining Human Emotion . Many emotions appear early in life and do not have to be learned. Evolutionary psychology suggests that emotions have evolved in response to selective pressures. For example, fear may have evolved to avoid potential threats to survival.
  • The Origins of Mental Health Problems . Behavioral traits like anxiety could have been adaptive in certain situations. For example, being worried and vigilant could have been very adaptive to survival and reproductive success if you lived in a time that involved many predators and dangers. However, too much anxiety could be maladaptive and harmful.
  • Understanding Parental Attachment . Attachment theory is well-established in developmental psychology. Human infants are very dependent on their parents, much more so than many other species. Evolutionary psychology, therefore, proposes that attachment between a parent and child has arisen due to its importance for survival and reproduction.  
  • Evolutionary Basis for Human Personality . Evolutionary psychology proposes that some personality traits, like aggression, have persisted since they were once valuable in competition for resources and mates.  
  • Explanation for Cooperation in Humans . Some people are more aggressive, while others are more agreeable and cooperative. Evolutionary psychology suggests that humans have evolved to be cooperative with others to increase their chances of survival. For example, cooperative behavior could have increased access to resources, reduced potentially harmful fighting, and increased help with childcare. 
  • Evolutionary Basis of Social Bonds . Humans are very social creatures. Evolutionary psychology proposes that humans have evolved to form strong social bonds because these bonds were important for gathering resources, taking care of each other, and surviving. 
  • Evolutionary Basis of Language . Human children start learning language and communication very early on. Evolutionary psychology proposes that language development occurs because the ability to communicate would have been useful for many activities that would have increased survival. For example, these activities could have involved warning others about danger, coordinating group activities, and passing along other useful information.
  • Explaining Behavioral Preferences through Evolution . Humans have many behavioral preferences. For example, many people enjoy what are now deemed “unhealthy” calorie-dense sweet and fatty foods. Evolutionary psychology would suggest that we have evolved preferences for these foods because these high-calorie foods were once particularly valuable sources of energy in our ancestral environment where food was often scarce. 

Criticisms of Evolutionary Biology

Human behavior is very complex and influenced by many biological, environmental, and cultural factors . Therefore, evolutionary psychology has faced some criticism and, like any psychological field, has important limitations to consider.

For example, many human behaviors persist that are not beneficial to survival and reproduction.

Additionally, we lack knowledge on the details of all the selection pressures humans could have faced over millions of years of evolution (Confer et al., 2010). This lack of knowledge and heavy reliance on theorizing leads to a lack of testability – we weren’t there to observe selective pressures millions of years ago.

As a result, we can’t directly test how those pressures may have shaped behavior.

Evolutionary psychology has also faced criticism for overemphasizing the role of biology in behavior.

However, we know that genetic and environmental influences are important to understand why humans differ from each other (Polderman et al., 2015).

The nature vs. nurture question that is so popular is somewhat misleading, as at this point, we know that nature and nurture are both essential and often interact with each other.

Other Types of Psychology

  • Biological Psychology – Biological psychology involves studying biological influences on behavior, thoughts, and emotions (Kalat, 2015).
  • Clinical Psychology – Clinical Psychology is a specialty in psychology that involves the practical application of psychological theories for treating psychological problems and disorders (Pomerantz, 2016).

Evolutionary psychologists operate under the assumption that human brain structures, functions, and mental capabilities evolved under natural selection in the same way that human bodies did (Mealey, 2023).

This would mean that the mental processes that underlie thought and behavior in humans exist now because they once helped human ancestors survive and reproduce.

Evolutionary psychological theories are applied to all human behavior, including emotions, personality, perception, and learning.

Buss, D. M. (2023). Evolutionary theories in psychology. In R. Biswas-Diener & E. Diener (Eds),  Noba textbook series: Psychology.  Champaign, IL: DEF publishers. Retrieved from  http://noba.to/ymcbwrx4

Confer, J. C., Easton, J. A., Fleischman, D. S., Goetz, C. D., Lewis, D. M. G., Perilloux, C., & Buss, D. M. (2010). Evolutionary psychology: Controversies, questions, prospects, and limitations. American Psychologist , 65 (2), 110–126. https://doi.org/10.1037/a0018413

Mealey, L. (2023). Evolutionary psychology. In Salem Press Encyclopedia of Health .

Polderman, T. J. C., Benyamin, B., de Leeuw, C. A., Sullivan, P. F., van Bochoven, A., Visscher, P. M., & Posthuma, D. (2015). Meta-analysis of the heritability of human traits based on fifty years of twin studies. Nature Genetics , 47 (7), 702–709. https://doi.org/10.1038/ng.3285

Workman, L. (2004). Evolutionary psychology: An introduction . Cambridge, UK ; New York : Cambridge University Press. http://archive.org/details/evolutionarypsyc0000work

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Evolutionary Psychology Research Paper Topics

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View the list of evolutionary psychology research paper topics. Read about the history of evolutionary psychology. Check other research paper topics for more inspiration. If you need a psychology research paper written according to all the academic standards, you can always turn to our experienced writers for help. This is how your paper can get an A! Feel free to contact our writing service for professional assistance. We offer high-quality assignments for reasonable rates.

Foundations of Evolutionary Psychology

  • The Theoretical Foundations of Evolutionary Psychology
  • Life History Theory and Evolutionary Psychology
  • Methods of Evolutionary Sciences
  • Evolutionary Psychology and Its Critics
  • Intuitive Ontologies and Domain Specificity

Evolutionary Psychology of Survival

  • The Evolutionary Psychology of Food Intake and Choice
  • The Behavioral Immune System
  • Spatial Navigation and Landscape Preferences
  • Adaptations to Predators and Prey
  • Adaptations to Dangers from Humans

Evolutionary Psychology of Mating

  • Adaptationism and Human Mating Psychology
  • Fundamentals of Human Mating Strategies
  • Physical Attractiveness
  • Contest Competition in Men
  • Women’s Sexual Interests Across the Ovulatory Cycle
  • Human Sperm Competition
  • Human Sexuality and Inbreeding Avoidance
  • Sexual Coercion
  • Love and Commitment in Romantic Relationships

Evolutionary Psychology of Parenting and Kinship

  • Kin Selection
  • Evolution of Paternal Investment
  • Parental Investment and Parent-Offspring Conflict
  • The Evolutionary Ecology of the Family
  • Hunter-Gatherer Families and Parenting
  • The Role of Hormones in the Evolution of Human Sociality

Evolutionary Psychology of Group Living: Cooperation and Conflict

  • Adaptations for Reasoning About Social Exchange
  • Interpersonal Conflict and Violence
  • Women’s Competition and Aggression
  • Prejudices: Managing Perceived Threats to Group Life
  • Leadership in War: Evolution, Cognition, and the Military Intelligence Hypothesis

Evolutionary Psychology of Culture and Coordination

  • Cultural Evolution
  • The Evolutionary Foundations of Status Hierarchy
  • The Evolution and Ontogeny of Ritual
  • The Origins of Religion
  • The False Allure of Group Selection

Evolutionary Psychology Interfaces with Traditional Psychology Disciplines

  • Evolutionary Cognitive Psychology
  • Evolutionary Developmental Psychology
  • Evolutionary Social Psychology
  • The General Factor of Personality: A Hierarchical Life History Model
  • The Evolution of Cognitive Bias
  • Biological Function and Dysfunction: Conceptual Foundations of Evolutionary Psychopathology
  • Evolutionary Psychology and Mental Health

Evolutionary Psychology Interfaces Across Traditional Academic Disciplines

  • Evolutionary Psychology and Evolutionary Anthropology
  • Evolutionary Genetics
  • Evolutionary Psychology and Endocrinology
  • Evolutionary Political Psychology
  • Evolutionary Literary Study

Practical Applications of Evolutionary Psychology

  • Evolutionary Psychology and Public Policy
  • Evolution and Consumer Psychology
  • Evolution and Organizational Leadership
  • Evolutionary Psychology and the Law

History of Evolutionary Psychology

Evolutionary psychology is the application of the principles and knowledge of evolutionary biology to psychological theory and research. Its central assumption is that the human brain is comprised of a large number of specialized mechanisms that were shaped by natural selection over vast periods of time to solve the recurrent information-processing problems faced by our ancestors (Symons, 1995).These problems include such things as choosing which foods to eat, negotiating social hierarchies, dividing investment among offspring, and selecting mates. The field of evolutionary psychology focuses on identifying these information-processing problems, developing models of the brain-mind mechanisms that may have evolved to solve them, and testing these models in research (Buss, 1995; Tooby & Cosmides, 1992).

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The field of evolutionary psychology has emerged dramatically over the last 15 years, as indicated by exponential growth in the number of empirical and theoretical articles in the area (Table 1.1). These articles extend into all branches of psychology—from cognitive psychology (e.g., Cosmides, 1989; Shepard, 1992) to developmental psychology (e.g., Ellis, McFadyen-Ketchum, Dodge, Pettit, & Bates, 1999; Weisfeld, 1999), abnormal psychology (e.g., Mealey, 1995; Price, Sloman, Gardner, Gilbert, & Rhode, 1994), social psychology (e.g., Daly & Wilson, 1988; Simpson & Kenrick, 1997), personality psychology (e.g., Buss, 1991; Sulloway, 1996), motivation-emotion (e.g., Nesse & Berridge, 1997; Johnston, 1999), and industrial-organizational psychology (e.g., Colarelli, 1998; Studd, 1996). The first undergraduate textbook on evolutionary psychology was published in 1999 (Buss, 1999), and since then at least three other undergraduate textbooks have been published in the area (Barrett, Dunbar, & Lycett, 2002; Cartwright, 2000; Gaulin & McBurney, 2000).

Evolutionary Psychology Research Paper Table 1

In this research paper we provide an introduction to the field of evolutionary psychology. We describe the methodology that evolutionary psychologists use to explain human cognition and behavior. This description begins at the broadest level with a review of the basic, guiding assumptions that are employed by evolutionary psychologists. We then show how evolutionary psychologists apply these assumptions to develop more specific theoretical models that are tested in research. We use examples of sex and mating to demonstrate how evolutionary psychological theories are developed and tested.

Levels of Explanation in Evolutionary Psychology

Why do siblings fight with each other for parental attention? Why are men more likely than women to kill sexual rivals? Why are women most likely to have extramarital sex when they are ovulating? To address such questions, evolutionary psychologists employ multiple levels of explanation ranging from broad metatheoretical assumptions, to more specific middle-level theories, to actual hypotheses and predictions that are tested in research (Buss, 1995; Ketelaar & Ellis, 2000). These levels of explanation are ordered in a hierarchy (see Figure 1.1) and constitute the methodology that evolutionary psychologists use to address questions about human nature.

Evolutionary Psychology Research Paper Figure1

At the top of the hierarchy are the basic metatheoretical assumptions of modern evolutionary theory. This set of guiding assumptions, which together are referred to as evolutionary metatheory, provide the foundation that evolutionary scientists use to build more specific theoretical models. We begin by describing (a) the primary set of metatheoretical assumptions that are consensually held by evolutionary scientists and (b) the special set of metatheoretical assumptions that distinguish evolutionary psychology. We use the term evolutionary psychological metatheory to refer inclusively to this primary and special set of assumptions together.

As shown in Figure 1.1, at the next level down in the hierarchy, just below evolutionary psychological metatheory, are middle-level evolutionary theories. These theories elaborate the basic metatheoretical assumptions into a particular psychological domain such as mating or cooperation. In this research paper we consider two related middle-level evolutionary theories—parental investment theory and good genes sexual selection theory—each of which applies the assumptions of evolutionary psychological metatheory to the question of reproductive strategies. In different ways these middle-level theories attempt to explain differences between the sexes as well as variation within each sex in physical and psychological adaptations for mating and parenting.

At the next level down are the actual hypotheses and predictions that are drawn from middle-level evolutionary theories (Figure 1.1). A hypothesis is a general statement about the state of the world that one would expect to observe if the theory from which it was generated were in fact true. Predictions are explicit, testable instantiations of hypotheses. We conclude this research paper with an evaluation of hypotheses and specific predictions about sexual behavior that have been derived from good genes sexual selection theory. Special attention is paid to comparison of human and nonhuman animal literatures.

The Metatheory Level of Analysis

Scientists typically rely on basic (although usually implicit) metatheoretical assumptions when they construct and evaluate theories. Evolutionary psychologists have often called on behavioral scientists to make explicit their basic assumptions about the origins and structure of the mind (see Gigerenzer, 1998). Metatheoretical assumptions shape how scientists generate, develop, and test middle-level theories and their derivative hypotheses and predictions (Ketelaar & Ellis, 2000). These basic assumptions are often not directly tested after they have been empirically established. Instead they are used as a starting point for further theory and research. Newton’s laws of motion form the metatheory for classical mechanics, the principles of gradualism and plate tectonics provide a metatheory for geology, and the principles of adaptation through natural selection provide a metatheory for biology. Several scholars (e.g., Bjorklund, 1997; Richters, 1997) have argued that the greatest impediment to psychology’s development as a science is the absence of a coherent, agreed-upon metatheory.

A metatheory operates like a map of a challenging conceptual terrain. It specifies both the landmarks and the boundaries of that terrain, suggesting which features are consistent and which are inconsistent with the core logic of the metatheory. In this way a metatheory provides a set of powerful methodological heuristics: “Some tell us what paths to avoid (negative heuristic), and others what paths to pursue (positive heuristic)” (Lakatos, 1970, p. 47). In the hands of a skilled researcher, a metatheory “provides a guide and prevents certain kinds of errors, raises suspicions of certain explanations or observations, suggests lines of research to be followed, and provides a sound criterion for recognizing significant observations on natural phenomena” (Lloyd, 1979, p. 18). The ultimate contribution of a metatheory is that it synthesizes middle-level theories, allowing the empirical results of a variety of different theory-driven research programs to be explicated within a broader metatheoretical framework. This facilitates systematic cumulation of knowledge and progression toward a coherent big picture, so to speak, of the subject matter (Ketelaar & Ellis, 2000).

Metatheoreticalassumptions That Are Consensually Held By Evolutionary Scientists

When asked what his study of the natural world had revealed about the nature of God, biologist J. B. S. Haldane is reported to have made this reply: “That he has an inordinate fondness for beetles.” Haldane’s retort refers to the extraordinary diversity of beetle species found throughout the world—some 290,000 species have so far been discovered (E. O. Wilson, 1992). Beetles, moreover, come in a bewildering variety of shapes and sizes, from tiny glittering scarab beetles barely visible to the naked eye to ponderous stag beetles with massive mandibles half the size of their bodies. Some beetles make a living foraging on lichen and fungi; others subsist on a diet of beetles themselves.

The richness and diversity of beetle species are mirrored throughout the biological world. Biologists estimate that anywhere from 10 to 100 million different species currently inhabit the Earth (E. O. Wilson, 1992), each one in some respect different from all others. How are we to explain this extraordinary richness of life? Why are there so many species and why do they have the particular characteristics that they do? The general principles of genetical evolution drawn from modern evolutionary theory, as outlined by W. D. Hamilton (1964) and instantiated in more contemporary so-called selfish gene theories of genetic evolution via natural and sexual selection, provide a set of core metatheoretical assumptions for answering these questions. Inclusive fitness theory conceptualizes genes or individuals as the units of selection (see Dawkins, 1976; Hamilton, 1964; Williams, 1966). In contrast, “multilevel selection theory” is based on the premise that natural selection is a hierarchical process that can operate at many levels, including genes, individuals, groups within species, or even multi-species ecosystems. Thus, multilevel selection theory is conceptualized as an elaboration of inclusive fitness theory (adding the concept of group-level adaptation) rather than an alternative to it (D. S. Wilson & Sober, 1994). Whereas inclusive fitness theory is consensually accepted among evolutionary scientists, multilevel selection theory is not. Thus, this review of basic metatheoretical assumptions only focuses on inclusive fitness theory.

Natural Selection

During his journey around the coastline of South America aboard the HMS Beagle, Charles Darwin was intrigued by the sheerdiversityofanimalandplantspeciesfoundinthetropics, by the way that similar species were grouped together geographically, and by their apparent fit to local ecological conditions. Although the idea of biological evolution had been around for some time, what had been missing was an explanation of how evolution occurred—that is, what had been missing was an account of the mechanisms responsible for evolutionary change. Darwin’s mechanism, which he labeled natural selection, served to explain many of the puzzling facts about the biological world: Why were there so many species? Why are current species so apparently similar in many respects both to each other and to extinct species? Why do organisms have the specific characteristics that they do?

The idea of natural selection is both elegant and simple, and can be neatly encapsulated as the result of the operation of three general principles: (a) phenotypic variation, (b) differential fitness, and (c) heritability.

As is readily apparent when we look around the biological world, organisms of the same species vary in the characteristics that they possess; that is, they have slightly different phenotypes. A whole branch of psychology—personality and individual differences—is devoted to documenting and understanding the nature of these kinds of differences in our own species. Some of these differences found among members of a given species will result in differences in fitness — that is, some members of the species will be more likely to survive and reproduce than will others as a result of the specific characteristics that they possess. For evolution to occur, however, these individual differences must be heritable — that is, they must be reliably passed on (via shared genes) from parents to their offspring. Over time, the characteristics of a population of organisms will change as heritable traits that enhance fitness will become more prevalent at the expense of less favorable variations.

For example, consider the evolution of bipedalism in humans. Paleoanthropological evidence suggests that upright walking (at least some of the time) was a feature of early hominids from about 3.5 million years ago (Lovejoy, 1988). Presume that there was considerable variation in the propensity to walk upright in the ancestors of this early hominid species as the result of differences in skeletal structures, relevant neural programs, and behavioral proclivities. Some hominids did and some did not.Also presume that walking on two feet much of the time conferred some advantage in terms of survival and reproductive success. Perhaps, by freeing the hands, bipedalism allowed objects such as meat to be carried long distances (e.g., Lovejoy, 1981). Perhaps it also served to cool the body by reducing the amount of surface area exposed to the harsh tropical sun, enabling foraging throughout the hottest parts of the day (e.g., Wheeler, 1991). Finally, presume that these differences in the propensity for upright walking were heritable in nature—they were the result of specific genes that were reliably passed on from parents to offspring.The individuals who tended to walk upright would be, on average, more likely to survive (and hence, to reproduce) than would those who did not. Over time the genes responsible for bipedalism would become more prevalent in the population as the individuals who possessed them were more reproductively successful than were those who did not, and bipedalism itself would become pervasive in the population.

Several points are important to note here. First, natural selection shapes not only the physical characteristics of organisms, but also their behavioral and cognitive traits. The shift to bipedalism was not simply a matter of changes in the anatomy of early hominids; it was also the result of changes in behavioral proclivities and in the complex neural programs dedicated to the balance and coordination required for upright walking. Second, although the idea of natural selection is sometimes encapsulated in the slogan the survival of the fittest, ultimately it is reproductive fitness that counts. It doesn’t matter how well an organism is able to survive. If it fails to pass on its genes, then it is an evolutionary dead end, and the traits responsible for its enhanced survival abilities will not be represented in subsequent generations. This point is somewhat gruesomely illustrated by many spider species in which the male serves as both meal and mate to the female—often at the same time. Ultimately, although one must survive to reproduce, reproductive goals take precedence.

Natural selection is the primary process which is responsible for evolutionary change over times as more favorable variants are retained and less favorable ones are rejected (Darwin, 1859). Through this filtering process, natural selection produces small incremental modifications in existing phenotypes, leading to an accumulation of characteristics that are organized to enhance survival and reproductive success. These characteristics that are produced by natural selection are termed adaptations. Adaptations are inherited and reliably developing characteristics of species that have been selected for because of their causal role in enhancing the survival and reproductive success of the individuals that possess them (see Buss, Haselton, Shackelford, Bleske, & Wakefield, 1998; Dawkins, 1986; Sterelny & Griffiths, 1999; Williams, 1966, 1992, for definitions of adaptation).

Adaptations have biological functions. The immune system functions to protect organisms from microbial invasion, the heart functions as a blood pump, and the cryptic coloring of many insects has the function of preventing their detection by predators. The core idea of evolutionary psychology is that many psychological characteristics are adaptations—just as many physical characteristics are—and that the principles of evolutionary biology that are used to explain our bodies are equally applicable to our minds. Thus, various evolutionary psychological research programs have investigated psychological mechanisms—for mate selection, fear of snakes, face recognition, natural language, sexual jealousy, and so on—as biological adaptations that were selected for because of the role they played in promoting reproductive success in ancestral environments.

It is worth noting, however, that natural selection is not the only causal process responsible for evolutionary change (e.g., Gould & Lewontin, 1979). Traits may also become fixated in a population by the process of genetic drift, whereby neutral or even deleterious characteristics become more prevalent due to chance factors. This may occur in small populations because the fittest individuals may turn out—due to random events—not to be the ones with the greatest reproductive success. It does not matter how fit you are if you drown in a flood before you get a chance to reproduce. Moreover, some traits may become fixated in a population not because they enhance reproductive success, but because they are genetically or developmentally yoked to adaptations that do. For example, the modified wrist bone of the panda (its “thumb”) seems to be an adaptation for manipulating bamboo, but the genes responsible for this adaptation also direct the enlarged growth of the corresponding bone in the panda’s foot, a feature that serves no function at all (Gould, 1980).

There is much debate among evolutionary biologists and philosophers of biology regarding the relative importance of different evolutionary processes (see Sterelny & Griffiths, 1999, for a good introduction to these and other issues in the philosophy of biology). The details of these disputes, however, need not concern us here. What is important to note is that not all of the products of evolution will be biological adaptations with evolved functions. The evolutionary process also results in by-products of adaptations, as well as a residue of noise (Buss et al., 1998; Tooby & Cosmides, 1992). Examples of by-products are legion. The sound that hearts make when they beat, the white color of bones, and the human chin are all nonfunctional by-products of natural selection. In addition, random variation in traits—as long as this variation is selectively neutral (neither enhancing nor reducing biological fitness)—can also be maintained as residual noise in organisms.

Demarcating the different products of evolution is an especially important task for evolutionary psychologists. It has often been suggested that many of the important phenomena that psychologists study—for example, reading, writing, religion—are by-products of adaptations rather than adaptations themselves (e.g., Gould, 1991a). Of course, even byproducts can be furnished with evolutionary explanations in terms of the adaptations to which they are connected (Tooby & Cosmides, 1992). Thus, for example, the whiteness of bones is a by-product of the color of calcium salts, which give bones their hardness and rigidity; the chin is a byproduct of two growth fields; and reading and writing are by-products (in part) of the evolved mechanisms underlying human language (Pinker, 1994).

The important question is how to distinguish adaptations from nonadaptations in the biological world. Because we cannot reverse time and observe natural selection shaping adaptations, we must make inferences about evolutionary history based on the nature of the traits we see today. A variety of methods can (and should) be employed to identify adaptations (see M. R. Rose & Lauder, 1996). Evolutionary psychologists, drawing on the work of George Williams (1966), typically emphasize the importance of special design features such as economy, efficiency, complexity, precision, specialization, reliability, and functionality for identifying adaptations (e.g., Buss et al., 1998; Pinker, 1997; Tooby & Cosmides, 1990). One hallmark that a trait is the product of natural selection is that it demonstrates adaptive complexity —that is, the trait is composed of a number of interrelated parts or systems that operate in concert to generate effects that serve specific functions (Dawkins, 1986; Pinker, 1997).

Echolocation in bats is a good example of such a trait. A collection of interrelated mechanisms allows foraging bats to maneuver around obstacles in complete darkness and to pick out small rapidly moving prey on the wing. Echolocating bats have a number of specialized mechanisms that precisely, reliably, and efficiently enable them to achieve the function of nocturnal locomotion and foraging. Bats have mechanisms that allow them to produce rapid, high-frequency, shortwavelength cries that are reflected by small objects. Moreover, the frequency and rapidity of these cries are modified depending on the distance of the object being detected (lowfrequency waves penetrate further but can only be used to detect large objects). Bats also have specialized mechanisms that protect their ears while they are emitting loud sounds, and their faces are shaped to enhance the detection of their returning echoes. It is extraordinary unlikely that such a complex array of intertwining processes could have arisen by chance or as a by-product of evolutionary processes. Thus, one has clear warrant in this case to assert that echolocation in bats is a biological adaptation.

Many traits, however, may not be so clearly identifiable as adaptations. Furthermore, there are often disputes about just what function some trait has evolved to serve, even if one can be reasonably sure that it is the product of natural selection. In adjudicating between alternative evolutionary hypotheses, one can follow the same sort of strategies that are employed when comparing alternative explanations in any domain in science—that is, one should favor the theory or hypothesis that best explains the evidence at hand (Haig & Durrant, 2000; Holcomb, 1998) and that generates novel hypotheses that lead to new knowledge (Ketelaar & Ellis, 2000).

Consider, for example, the alternative explanations that have been offered for the origin of orgasm in human females.

  • Female orgasm serves no evolved function and is a byproduct of selection on male orgasm, which is necessary for fertilization to occur (Gould, 1991b, pp. 124–129; Symons, 1979).
  • Orgasm is an adaptation that promotes pair-bonding in the human species (Eibl-Eibesfeldt, 1989).
  • Female orgasm is an adaptation that motivates females to seek multiple sexual partners, confusing males about paternity and thus reducing the probability of subsequent male infanticide (Hrdy, 1981).
  • Female orgasm is an adaptation that serves to enhance sperm retention, therefore allowing females to exert some control over the paternity of their offspring via differential patterns of orgasm with specific male partners, especially those of high genetic quality (Baker & Bellis, 1993; Smith, 1984).

Although all of these models have some plausibility, it is the last suggestion that is beginning to be accepted as the best current explanation. Baker and Bellis (1993) have demonstrated that females retain more sperm if they experience copulatory orgasms up to 45 min after—or at the same timeas—their male partners. Thus, depending on their timing, orgasms appear to enhance the retention of sperm via the “upsuck” from the vagina into the cervix. The selective sperm retention model predicts that women will experience more orgasms—and specifically, more high-sperm-retention orgasms—with men who have specific indicators of genetic quality.This prediction has been supported in research on dating and married couples (Thornhill, Gangestad, & Comer, 1995). Moreover, the occurrence of high sperm retention orgasms are a significant predictor of a desire for pregnancy in women, suggesting that female orgasms are one mechanism for increasing the likelihood of conception (Singh, Meyer, Zambarano, & Hurlbert, 1998).

Although there are a number of theories of extrapair mating in human females (mating that occurs outside of a current, ongoing relationship), one prominent suggestion is that extrapair mating has evolved to enhance reproductive success by increasing selective mating with males who demonstrate high genetic quality (e.g., Gangestad, 1993; Greiling & Buss, 2000). In support of this idea, men who possess indicators of high genetic quality (as assessed by degree of symmetry of bilateral physical traits) are more likely to be chosen by women specifically as extrapair sex partners but not as partners in long-term relationships (Gangestad & Simpson, 2000). Further, Bellis and Baker (1990) found that women were most likely to copulate with extrapair partners but not with in-pair partners during the fertile phase of their menstrual cycles. Finally, as a result of the type and frequency of orgasms experienced by women, it appears that levels of sperm retention are significantly higher during extrapair copulations than during copulations with in-pair partners (Baker & Bellis, 1995).

In summary, although more research needs to be done, our best current explanation for the human female orgasm is that it is an adaptation specifically, precisely, and efficiently designed to manipulate the paternity of offspring by favoring the sperm of males of high genetic quality.This model (a) concurs with what is known about female orgasm; (b) generated specific, testable predictions about patterns of variation in female orgasm that were as yet unobserved and were not forecast by competing models; (c) generated interesting new lines of research on female orgasm that provided support for the predictions; and (d) led to acquisition of new knowledge about the timing and probability of female orgasm with different partners.

Sexual Selection

Not all adaptations can be conceptualized as adaptations for survival per se.Although the bat’s complex system of echolocation enables it to navigate and forage in darkness, the human female orgasm has no such obvious utilitarian function.As Darwin (1871) clearly recognized, many of the interesting features that plants and animals possess, such as the gaudy plumage and elaborate songs of many male birds, serve no obvious survival functions. In fact, if anything, such traits are likely to reduce survival prospects by attracting predators, impeding movement, and so on. Darwin’s explanation for such characteristics was that they were the product of a process that he labeled sexual selection. This kind of selection arises not from a struggle to survive, but rather from the competition that arises over mates and mating (Andersson, 1994; Andersson & Iwasa, 1996). If—for whatever reason—having elongated tail feathers or neon blue breast plumage enables one to attract more mates, then such traits will increase reproductive success. Moreover, to the extent that such traits are also heritable, they will be likely to spread in the population, even if they might diminish survival prospects.

Although there is some debate about how best to conceptualize the relationship between natural and sexual selection, sexual selection is most commonly considered a component or special case of natural selection associated with mate choice and mating. This reflects the fact that differential fitness concerns differences in both survival and reproduction. Miller (1999) notes that “both natural selection and sexual selection boil down to one principle: Some genes replicate themselves better than others. Some do it by helping their bodies survive better, and some by helping themselves reproduce better” (p. 334). Whereas the general processes underlying natural and sexual selection are the same (variation, fitness, heritability), the products of natural and sexual selection can look quite different. The later parts of this research paper review sexual selection theory and some of the exciting research it has generated on human mating behavior.

To summarize, we have introduced the ideas of natural and sexual selection and shown how these processes generate adaptations, by-products, and noise. We have also discussed ways in which adaptations can be distinguished from nonadaptations and have offered some examples drawn from recent research in evolutionary psychology. It is now time to consider an important theoretical advance in evolutionary theorizing that occurred in the 1960s—inclusive fitness theory— that changed the way biologists (and psychologists) think about the nature of evolution and natural selection. Inclusive fitness theory is the modern instantiation of Darwin’s theory of adaptation through natural and sexual selection.

Inclusive Fitness Theory

Who are adaptations good for? Although the answer may seem obvious—that they are good for the organisms possessing the adaptations—this answer is only partially correct; it fails to account for the perplexing problem of altruism. As Darwin puzzled, how could behaviors evolve that conferred advantage to other organisms at the expense of the principle organism that performed the behaviors? Surely such acts of generosity would be eliminated by natural selection because they decreased rather than increased the individual’s chances of survival and reproduction.

The solution to this thorny evolutionary problem was hinted at by J. B. S. Haldane, who, when he was asked if he would lay down his life for his brother, replied, “No, but I would for two brothers or eight cousins” (cited in Pinker, 1997, p. 400). Haldane’s quip reflects the fact that we each share (on average) 50% of our genes with our full siblings and 12.5% of our genes with our first cousins. Thus, from the gene’s-eye point of view, it is just as advantageous to help two of our siblings to survive and reproduce as it is to help ourselves. This insight was formalized by W. D. Hamilton (1964) and has come to be known variously as Hamilton’s rule, selfish-gene theory (popularized by Dawkins, 1976), kin-selection theory, or inclusive fitness theory.

The core idea of inclusive fitness theory is that evolution works by increasing copies of genes, not copies of the individuals carrying the genes. Thus, the genetic code for a trait that reduces personal reproductive success can be selected for if the trait, on average, leads to more copies of the genetic code in the population. A genetic code for altruism, therefore, can spread through kin selection if (a) it causes an organism to help close relatives to reproduce and (b) the cost to the organism’s own reproduction is offset by the reproductive benefit to those relatives (discounted by the probability that the relatives who receive the benefit have inherited the same genetic code from a common ancestor). For example, a squirrel who acts as a sentinel and emits loud alarm calls in the presence of a predator may reduce its own survival chances by directing the predator’s attention to itself; however, the genes that are implicated in the development of alarm-calling behavior can spread if they are present in the group of close relatives who are benefited by the alarm calling.

Special Metatheoretical Assumptions of Evolutionary Psychology

In addition to employing inclusive fitness theory, evolutionary psychologists endorse a number of special metatheoretical assumptions concerning how to apply inclusive fitness theory to human psychological processes. In particular, evolutionary psychologists argue that we should primarily be concerned with how natural and sexual selection have shaped psychological mechanisms in our species; that a multiplicity of such mechanisms will exist in the human mind; and that they will have evolved to solve specific adaptive problems encountered in ancestral environments. Although these general points also apply to other species, they are perhaps especially pertinent in a human context and they have received much attention from evolutionary psychologists. We consider these special metatheoretical assumptions, in turn, in the following discussion.

Psychological Mechanisms as the Main Unit of Analysis

Psychological adaptations, which govern mental and behavioral processes, are referred to by evolutionary psychologists as psychological mechanisms. Evolutionary psychologists emphasize that genes do not cause behavior and cognition directly. Rather, genes provide blueprints for the construction of psychological mechanisms, which then interact with environmental factors to produce a range of behavioral and cognitive outputs. Most research in evolutionary psychology focuses on identifying evolved psychological mechanisms because it is at this level where invariances occur. Indeed, evolutionary psychologists assert that there is a core set of universal psychological mechanisms that comprise our shared human nature (Tooby & Cosmides, 1992).

To demonstrate the universal nature of our psychological mechanisms, a common rhetorical device used by evolutionary psychologists (e.g., Brown, 1991; Ellis, 1992; Symons, 1987) is to imagine that a heretofore unknown tribal people is suddenly discovered. Evolutionary psychologists are willing to make a array of specific predictions—in advance—about the behavior and cognition of this newly discovered people.These predictions concern criteria that determine sexual attractiveness, circumstances that lead to sexual arousal, taste preferences for sugar and fat, use of cheater detection procedures in social exchange, nepotistic bias in parental investment and child abuse, stages and timing of language development, sex differences in violence, different behavioral strategies for people high and low in dominance hierarchies, perceptual adaptations for entraining, tracking, and predicting animate motion, and so on. The only way that the behavior and cognition of an unknown people can be known in advance is if we share with those people a universal set of specific psychological mechanisms.

Buss (1999, pp. 47–49) defines an evolved psychological mechanism as a set of structures inside our heads that (a) exist in the form they do because they recurrently solved specific problems of survival and reproduction over evolutionary history; (b) are designed to take only certain kinds of information from the world as input; (c) process that information according to a specific set of rules and procedures; (d) generate output in terms of information to other psychological mechanisms and physiological activity or manifest behavior that is directed at solving specific adaptive problems (as specified by the input that brought the psychological mechanism on-line).

Consider, for example, the psychological mechanisms underlying disgust and food aversions in humans. These psychological mechanisms, which are designed to find certain smells and tastes more aversive than others, can be said to have several features:

  • They exist in the form they do because they recurrently solved specific problems of survival over evolutionary history. As an omnivorous species, humans consume a wide variety of plant and animal substances. Not all such substances, however, are safe to eat. Many plants contain natural toxins, and many animal products are loaded with parasites that can cause sickness and death. The psychological mechanisms underlying disgust and food aversions function to reduce the probability of ingesting and digesting dangerous plant and animal substances.
  • These mechanisms are designed to take a specific and limited class of stimuli as input: the sight, touch, and especially taste and smell of plant and animal substances that were regularly harmful to our ancestors. Feces and animal products are especially likely to harbor lethal microorganisms and, cross-culturally, are most likely to elicit disgust (Rozin & Fallon, 1987).
  • Inputs to the psychological mechanisms underlying disgust and food aversions are then processed according to a set of decision rules and procedures, such as (a) avoid plant substances that taste or smell bitter or especially pungent (indicating high concentrations of plant toxins; Profet, 1992); (b) avoid animal substances that emit smells suggestive of spoilage (indicating high levels of toxinproducing bacteria; Profet, 1992); (c) avoid foods that one has become sick after consuming in the past (Seligman & Hager, 1972); (d) and avoid foods that were not part of one’s diet in the first few years of life (especially if it is an animal product; Cashdan, 1994).
  • When relevant decision rules are met, behavioral output is then generated, manifested by specific facial expressions, physical withdrawal from the offending stimuli, nausea, gagging, spitting, and vomiting.
  • This output is specifically directed at solving the adaptive problem of avoiding consumption of harmful substances and of expelling these substances from the body as rapidly as possible if they have been consumed.

Evolutionary psychologists assume that humans possess a large number of specific psychological mechanisms (e.g., the ones underlying food aversions and disgust) that are directed at solving specific adaptive problems. This assumption is commonly referred to as the domain specificity or modularity of mind.

Domain Specificity of Psychological Mechanisms

Evolutionary psychologists posit that the mind comprises a large number of content-saturated ( domain-specific ) psychological mechanisms (e.g., Buss, 1995; Cosmides & Tooby, 1994; Pinker, 1997). Although evolutionary psychologists assert that the mind is not comprised primarily of content-free ( domain-general ) psychological mechanisms, it is likely that different mechanisms differ in their levels of specificity and that there are some higher-level executive mechanisms that function to integrate information across more specific lowerlevel mechanisms.

The rationale behind the domain-specificity argument is fairly straightforward: What counts as adaptive behavior differs markedly from domain to domain. The sort of adaptive problems posed by food choice, mate choice, incest avoidance, and social exchange require different kinds of solutions. As Don Symons (1992) has pointed out, there is no such thing as a general solution because there is no such thing as a general problem. The psychological mechanisms underlying disgust and food aversions, for example, are useful in solving problems of food choice but not those of mate choice. If we used the same decision rules in both domains, we would end up with some very strange mates and very strange meals indeed. Given the large array of adaptive problems faced by our ancestors, we should expect a commensurate number of domain-specific solutions to these problems.

A clear analogy can be drawn with the functional division of labor in human physiology. Different organs have evolved to serve different functions and possess properties that allow them to fulfill those functions efficiently, reliably, and economically: The heart pumps blood, the liver detoxifies poisons, the kidneysexcreteurine,andsoon.Asuper,all-purpose,domaingeneral internal organ—heart, liver, kidney, spleen, and pancreas rolled into one—faces the impossible task of serving multiple, incompatible functions. Analogously, a super, allpurpose, domain-general brain-mind mechanism faces the impossible task of efficiently and reliably solving the plethora of behavioral problems encountered by humans in ancestral environments. Thus, neither an all-purpose physiological organ nor an all-purpose brain-mind mechanism is likely to evolve. Evolutionary psychologists argue that the human brain-mind instead contains domain-specific information processing rules and biases.

These evolved domain-specific mechanisms are often referred to as psychological modules. The best way to conceptualize such modules, however, is a matter of some contention. Jerry Fodor (1983), in his classic book The Modularity of Mind, suggests that modules have the properties of being domain-specific, innately specified, localized in the brain, and able to operate relatively independently from other such systems. Potentially good examples of such psychological modules in humans include language (Pinker, 1994), face recognition (Bruce, 1988), and theory of mind (Baron-Cohen, 1995). For example, the systems underlying language ability are specially designed to deal with linguistic information, emerge in development with no formal tuition, and appear to be located in specific brain regions independent from other systems, as indicated by specific language disorders (aphasias), which can arise from localized brain damage.

Not all of the evolved psychological mechanisms proposed by evolutionary psychologists, however, can be so readily characterized. Many mechanisms—such as landscape preferences, sexual jealousy, and reasoning processes—may be domain-specific in the sense of addressing specific adaptive problems, but they are neither clearly localized (neurally speaking) nor especially autonomous from other systems. It seems most plausible to suggest that there is a considerable degree of integration and interaction between different psychological mechanisms (Karmiloff-Smith, 1992). It is this feature of human cognitive organization that allows for the tremendous flexibility and creativity of human thought processes (Browne, 1996). It is also not clear whether domain specificity is best characterized by way of specific computational mechanisms or in terms of domain-specific bodies of mental representations (Samuels, 2000).

We should also expect—in addition to whatever taxonomy of specialized mechanisms that is proposed for the human mind—that there are some domain-general processes as well. The mechanisms involved in classical and operant conditioning may be good candidates for such domain-general processes. However, even these domain-general processes appear to operate in different ways, depending on the context in question. As illustrated in a series of classic studies by Garcia and colleagues (e.g., Garcia & Koelling, 1966), rats are more likely to develop some (adaptively relevant) associations than they are others, such as that between food and nausea but not between buzzers and nausea. Similar prepared learning biases have been demonstrated in monkeys (Mineka, 1992) and also in humans (Seligman & Hagar, 1972). For example, humans are overwhelmingly more likely to associate anxiety and fear with evolutionarily relevant threats such as snakes, spiders, social exclusion, and heights than with more dangerous but evolutionarily novel threats such as cars, guns, and power lines (Marks & Nesse, 1994).

In sum, although some doubt remains over the nature and number of domain-specific psychological mechanisms that humans (and other animals) possess, the core idea of specialized adaptive processes instantiated in psychological mechanisms remains central to evolutionary psychology. An approach to the human mind that highlights the importance of evolved domain-specific mechanisms can advance our understanding of human cognition by offering a theoretically guided taxonomy of mental processes—one that promises to better carve the mind at its natural joints.

The Environment of Evolutionary Adaptedness

The concept of biological adaptation is necessarily an historical one. When we claim that the thick insulating coat of the polar bear is as an adaptation, we are claiming that possession of that trait advanced reproductive success in ancestral environments. All claims about adaptation are claims about the past because natural selection is a gradual, cumulative process. The polar bear’s thick coat arose through natural selection because it served to ward off the bitter-cold arctic weather during the polar bear’s evolutionary history. However, traits that served adaptive functions and thus were selected for in past environments may not still be adaptive in present or future environments. In a globally warmed near-future, for example, the polar bear’s lustrous pelt may become a handicap that reduces the fitness of its owner due to stress from overheating. In sum, when environments change, the conditions that proved advantageous to the evolution of a given trait may no longer exist; yet the trait often remains in place for some time because evolutionary change occurs slowly. Such vestigial traits are eventually weeded out by natural selection (if they consistently detract from fitness).

The environment in which a given trait evolved is termed its environment of evolutionary adaptedness (EEA). The EEAfor our species is sometimes loosely characterized as the Pleistocene—the 2-million-year period that our ancestors spent as hunter-gatherers in the African savanna, prior to the emergence of agriculture some 10,000 years ago. The emphasis on the Pleistocene is perhaps reasonable given that many of the evolved human characteristics of interest to psychologists, such as language, theory of mind, sophisticated tool use, and culture, probably arose during this period. However, a number of qualifications are in order. First, the Pleistocene itself captures a large span of time, in which many changes in habitat, climate and species composition took place. Second, there were a number of different hominid species in existence during this time period, each inhabiting its own specific ecological niche. Third, many of the adaptations that humans possess have their origins in time periods that substantially predate the Pleistocene era. For example, the mechanisms underlying human attachment and sociality have a long evolutionary history as part of our more general primate and mammalian heritage (Foley, 1996). Finally, some evolution (although of a relatively minor character) has also probably occurred in the last 10,000 years, as is reflected in population differences in disease susceptibility, skin color, and so forth (Irons, 1998).

Most important is that different adaptations will have different EEAs. Some, like language, are firmly anchored in approximately the last 2 million years; others, such as infant attachment, reflect a much lengthier evolutionary history (Hrdy, 1999). It is important, therefore, that we distinguish between the EEA of a species and the EEA of an adaptation. Although these two may overlap, they need not necessarily do so (Crawford, 1998). Tooby and Cosmides (1990) summarize these points clearly when they state that “the ‘environment of evolutionary adaptedness’(EEA) is not a place or a habitat, or even a time period. Rather, it is a statistical composite of the adaptation-relevant properties of the ancestral environments encountered by members of ancestral populations, weighted by their frequency and fitness-consequences” (pp. 386–387). Delineating the specific features of the EEA for any given adaptation, then, requires an understanding of the evolutionary history of that trait (e.g., is it shared by other species, or is it unique?) and a detailed reconstruction of the relevant environmental features that were instrumental in its construction (Foley, 1996).

It is not uncommon to hear the idea that changes wrought by “civilization” over the last 10,000 years have radically changed our adaptive landscape as a species. After all, back on the Pleistocene savanna there were no fast food outlets, plastic surgery, antibiotics, dating advertisements, jet airliners, and the like. Given such manifest changes in our environment and ways of living, one would expect much of human behavior to prove odd and maladaptive as psychological mechanisms that evolved in ancestral conditions struggle with the many new contingencies of the modern world. An assumption of evolutionary psychology, therefore, is that mismatches between modern environments and the EEA often result in dysfunctional behavior (such as overconsumption of chocolate ice cream, television soap operas, video games, and pornography). Real-life examples of this phenomenon are easy to find. Our color constancy mechanisms, for instance, evolved under conditions of natural sunlight. These mechanisms fail, however, under some artificial lighting conditions (Shepard, 1992). Similarly, the dopaminemediated reward mechanisms found in the mesolimbic system in the brain evolved to provide a pleasurable reward in the presence of adaptively relevant stimuli like food or sex. In contemporary environments, however, these same mechanisms are subverted by the use of psychoactive drugs such as cocaine and amphetamines, which deliver huge dollops of pleasurable reward in the absence of the adaptively relevant stimuli—often to the users’ detriment (Nesse & Berridge, 1997).

Although we can detail many ways in which contemporary and ancestral environments differ, much probably also remains the same. Humans everywhere, for example, still find and attract mates, have sex, raise families, make friends, have extramarital affairs, compete for status, consume certain kinds of food, spend time with kin, gossip, and so forth (Crawford, 1998). Indeed, Crawford (1998) argues that we should accept as our null hypothesis that current and ancestral environments do not differ in important and relevant respects for any given adaptation. Most important is that current and ancestral environments do not have to be identical in every respect for them to be the same in terms of the relevant details required for the normal development and expression of evolved psychological mechanisms. For example, the languages that people speak today are undoubtedly different from the ones our ancestors uttered some 100,000 years ago. However, what is necessary for the development of language is not the input of some specific language, but rather any kind of structured linguistic input. Adaptations have reaction norms, which are the range of environmental parameters in which they develop and function normally. For most adaptations, these norms may well encompass both current and ancestral environments (Crawford, 1998).

To summarize, in this section we have outlined three special metatheoretical assumptions that evolutionary psychologists use in applying inclusive fitness theory to human cognition and behavior. First, the appropriate unit of analysis is typically considered to be at the level of evolved psychological mechanisms, which underlie behavioral output. Second, evolutionary psychologists posit that these mechanisms are both large in number and constitute specialized information processing rules that were designed by natural selection to solve specific adaptive problems encountered during human evolutionary history. Finally, these mechanisms have evolved in ancestral conditions and are characterized by specific EEAs, which may or may not differ in important respects from contemporary environments.

The Middle-Level Theory Level of Analysis

The metatheoretical assumptions employed by evolutionary psychologists are surrounded by a protective belt, so to speak, of auxiliary theories, hypotheses, and predictions (see Buss, 1995; Ketelaar & Ellis, 2000). A primary function of the protective belt is to provide an empirically verifiable means of linking metatheoretical assumptions to observable data. In essence, the protective belt serves as the problemsolving machinery of the metatheoretical research program because it is used to provide indirect evidence in support of the metatheory’s basic assumptions (Lakatos, 1970). The protective belt does more, however, than just protect the meta-theoretical assumptions: It uses these assumptions to extend our knowledge of particular domains. For example, a group of physicists who adopt a Newtonian metatheory may construct several competing middle-level theories concerning a particular physical system, but none of these theories would violate Newton’s laws of mechanics. Each physicist designs his or her middle-level theory to be consistent with the basic assumptions of the metatheory, even if the middlelevel theories are inconsistent with each other. Competing middle-level theories attempt to achieve the best operationalization of the core logic of the metatheory as it applies to a particular domain. The competing wave and particle theories of light (generated from quantum physics metatheory) are excellent contemporary exemplars of this process.

After a core set of metatheoretical assumptions become established among a community of scientists, the day-to-day workings of these scientists are generally characterized by the use of— not the testing of— these assumptions. Metatheoretical assumptions are used to construct plausible alternative middle-level theories. After empirical evidence has been gathered, one of the alternatives may emerge as the best available explanation of phenomena in that domain. It is this process of constructing and evaluating middle-level theories that characterizes the typical activities of scientists attempting to use a metatheory to integrate, unify, and connect their varying lines of research (Ketelaar & Ellis, 2000).

Middle-level evolutionary theories are specific theoretical models that provide a link between the broad metatheoretical assumptions used by evolutionary psychologists and the specific hypotheses and predictions that are tested in research. Middle-level evolutionary theories are consistent with and guided by evolutionary metatheory but in most cases cannot be directly deduced from it (Buss, 1995). Middle-level theories elaborate the basic assumptions of the metatheory into a particular psychological domain. For example, parental investment theory (Trivers, 1972) applies evolutionary metatheory to the question of why, when, for what traits, and to what degree selection favors differences between the sexes in reproductive strategies. Conversely, attachment theory (Bowlby, 1969; Simpson, 1999), life history theory (e.g., Chisholm, 1999), and good genes sexual selection theory (e.g., Gangestad & Simpson, 2000) each in different ways applies evolutionary metatheory to the question of why, when, for what traits, and to what degree selection favors differences within each sex in reproductive strategies. In this section we review parental investment theory and good genes sexual selection theory as exemplars of middle-level evolutionary theories.

Parental Investment Theory

Imagine that a man and a woman each had sexual intercourse with 100 different partners over the course of a year. The man could potentially sire 100 children, whereas the woman could potentially give birth to one or two. This huge discrepancy in the number of offspring that men and women can potentially produce reflects fundamental differences between the sexes in the costs of reproduction. Sperm, the sex cells that men produce, are small, cheap, and plentiful. Millions of sperm are produced in each ejaculate, and one act of sexual intercourse (in principle) is the minimum reproductive effort needed by a man to sire a child. By contrast, eggs, the sex cells that women produce, are large, expensive, and limited in number. Most critical is that one act of sexual intercourse plus 9 months gestation, potentially dangerous childbirth, and (in traditional societies) years of nursing and carrying a child are the minimum amount of reproductive effort required by a woman to successfully reproduce. These differences in what Trivers (1972) has termed parental investment have wide-ranging ramifications for the evolution of sex differences in body, mind, and behavior. Moreover, these differences hold true not only for humans but also for all mammalian species.

Trivers (1972) defined parental investment as “any investment by the parent in an individual offspring’s chance of surviving (and hence reproductive success) at the cost of the parent’s ability to invest in other offspring” (p. 139). Usually, but not always, the sex with the greater parental investment is the female. These differences in investment are manifest in various ways, from basic asymmetries in the size of male and female sex cells (a phenomenon known as anisogamy ) through to differences in the propensity to rear offspring. For most viviparous species (who bear live offspring), females also shoulder the burden of gestation—and in mammals, lactation and suckling. In terms of parental investment, the sex that invests the most becomes a limiting resource for the other, less investing sex (Trivers, 1972). Members of the sex that invests less, therefore, should compete among themselves for breeding access to the other, more investing sex. Because males of many species contribute little more than sperm to subsequent offspring, their reproductive success is primarily constrained by the number of fertile females that they can inseminate. Females, by contrast, are constrained by the number of eggs that they can produce and (in species with parental care) the number of viable offspring that can be raised. Selection favors males in these species who compete successfully with other males or who have qualities preferred by females that increase their mating opportunities. Conversely, selection favors females who choose mates who have good genes and (in paternally investing species) are likely to provide external resources such as food or protection to the female and her offspring (Trivers, 1972).

Parental investment theory, in combination with the metatheoretical assumptions of natural and sexual selection, generates an array of hypotheses and specific predictions about sex differences in mating and parental behavior. According to parental investment theory, the sex that invests more in offspring should be more careful and discriminating in mate selection, should be less willing to engage in opportune mating, and should be less inclined to seek multiple sexual partners. By contrast, the sex investing less in offspring should be less choosy about whom they mate with, compete more strongly among themselves for mating opportunities (i.e., take more risks and be more aggressive in pursuing sexual contacts), and be more inclined to seek multiple mating opportunities. The magnitude of these sex differences should depend on the magnitude of differences between males and females in parental investment during a species’ evolutionary history. In species in which males only contribute their sperm to offspring, males should be much more aggressive than should females in pursuing sexual contacts with multiple partners, and females should be much choosier than should males in accepting or rejecting mating opportunities. In contrast, in species such as humans in which both males and females typically make high levels of investment in offspring, sex differences in mating competition and behavior should be more muted. Nonetheless, the sex differences predicted by parental investment theory are well documented in humans as well as in many other animals. In humans, for example, men are more likely than are women to pursue casual mating opportunities and multiple sex partners, men tend to have less rigid standards than women do for selecting mates, and men tend to engage in more extreme intrasexual competition than women do (Buss, 1994; Daly & Wilson, 1988; Ellis & Symons, 1990; Symons, 1979).

Among mammalian species, human males are unusual insofar as they contribute nonnegligible amounts of investment to offspring. Geary (2000), in a review of the evolution and proximate expression of human paternal investment, has proposed that (a) over human evolutionary history fathers’ investment in families tended to improve but was not essential to the survival and reproductive success of children and (b) selection consequently favored a mixed paternal strategy, with different men varying in the extent to which they allocated resources to care and provisioning of children. Under these conditions, selection should favor psychological mechanisms in females that are especially attuned to variation in potential for paternal investment. This hypothesis has been supported by much experimental and cross-cultural data showing that when they select mates, women tend to place relatively strong emphasis on indicators of a man’s willingness and ability to provide parental investment (e.g., Buss, 1989; Ellis, 1992; Symons, 1979). These studies have typically investigated such indicators as high status, resourceaccruing potential, and dispositions toward commitment and cooperation.

The other side of the coin is that men who invest substantially in offspring at the expense of future mating opportunities should also be choosy about selecting mates. Men who provide high-quality parental investment (i.e., who provide valuable economic and nutritional resources; who offer physical protection; who engage in direct parenting activities such as teaching, nurturing, and providing social support and opportunities) are themselves a scarce resource for which women compete. Consequently, high-investing men should be as careful and discriminating as women are about entering long-term reproductive relationships. Along these lines, Kenrick, Sadalla, Groth, and Trost (1990) investigated men’s and women’s minimum standards for selecting both shortterm and long-term mates. Consistent with many other studies (e.g., Buss & Schmitt, 1993; Symons & Ellis, 1989), men were found to have minimum standards lower than those of women for short-term sexual relationships (e.g., one-night stands); however, men elevated their standards to levels comparable to those of women when choosing long-term mates (Kenrick et al., 1990).

Mate Retention Strategies

In species with internal fertilization (all mammals, birds, reptiles, and many fish and insects), males cannot identify their offspring with certainty. In such species, males who invest paternally run the risk of devoting time and energy to offspring who are not their own. Thus, male parental investment should only evolve as a reproductive strategy when fathers have reasonably high confidence of paternity—that is, males should be selected to be high-investing fathers only to offspring who share their genes. When male parental investment does evolve, selection should concomitantly favor the evolution of male strategies designed to reduce the chance of diverting parental effort toward unrelated young (Daly, Wilson, & Weghorst, 1982; Symons, 1979). Mate retention strategies (including anatomical and behavioral adaptations) are favored by sexual selection in paternally investing species because they increase the probability that subsequent investment made by fathers in offspring contributes to their own fitness and not to that of other males.

A fascinating array of mate retention strategies has been documented in many animal species. Male damselflies, for example, possess a dual-function penis that has special barbs that enables them to remove any sperm from prior matings before inseminating the female themselves. Furthermore, male damselflies remain physically attached to the female after mating until she has laid her eggs, thus ensuring that other males cannot fertilize them. In many species of birds with biparental care, males adjust their subsequent paternal investment (e.g., feeding of nestlings) depending on their degree of paternity certainty as determined by such factors as time spent with the mate and degree of extrapair matings in which she has engaged. The greater the likelihood that the offspring he is raising is not his own, the less investment is offered (e.g., Moller, 1994; Moller & Thornhill, 1998; but see Kempenaers, Lanctot, & Robertson, 1998). Sexual jealousy in humans has also been proposed as an evolved motivational system that underlies mate retention behaviors and functions to reduce the probability of relationship defection and to increase certainty of paternity in males (Buss, 2000; Daly et al., 1982). Daly et al. (1982) suggest that in men, pervasive mate retention strategies include “the emotion of sexual jealousy, the dogged inclination of men to possess and control women, and the use or threat of violence to achieve sexual exclusivity and control” (p. 11).

Females, of course, are not passive spectators to these male manipulations, but have evolved a host of strategies themselves to advance their own inclusive fitness. In many species females may try to extract investment from males through various means such as withholding sex until resources are provided, obscuring the time that they are fertile to encourage prolonged male attention, and preventing males from investing resources in multiple females. Furthermore, in some circumstances it may benefit females to extract material resources from one male while pursuing extrapair matings with other males who may be of superior genetic quality (see early discussion of the function of female orgasm; see also Buss, 1994; Greiling & Buss, 2000; for birds, see Moller & Thornhill, 1998; Petrie & Kempenaers, 1998).

Although the general pattern of greater female parental investment and less male parental investment is most common, a variety of species exhibit the opposite arrangement. For example, in a bird species called the red-necked phalarope, it is the male who takes on the burden of parental investment, both incubating and feeding subsequent offspring. As predicted by parental investment theory, it is the female in this species who is physically larger, who competes with other females for reproductive opportunities, and who more readily pursues and engages in multiple matings. In addition, levels of parental investment may vary within a species over time, with corresponding changes in mating behavior. For example, in katydids or bush crickets, males contribute to offspring by offering mating females highly nutritious sperm packages called spermatophores. When food resources are abundant, males can readily produce these spermatophores. Under these conditions, males compete with each other for mating access to females and readily pursue multiple mating opportunities. When food resources are scarce, however, spermatophores are costly to produce. Under these conditions, it is the females who compete with each other for mating access to males with the valued spermatophores, and it is females who more readily engage in multiple matings (see Andersson, 1994, pp. 100–103). These examples of so-called sex-role reversed species illustrate that sex differences do not arise from biological sex per se; rather, they arise from differences between the sexes in parental investment.

Parental investment theory is one of the most important middle-level theories that guides research into many aspects of human and animal behavior. Both the nature and the magnitude of sex differences in mating and parental behaviors can be explained by considering differences between the sexes in parental investment over a species’evolutionary history. A host of general hypotheses and specific predictions have been derived from considering the dynamics of parental investment and sexual selection, and much empirical evidence in both humans and other animals has been garnered in support of these hypotheses and predictions. Parental investment theory is one of the real triumphs of evolutionary biology and psychology and gives support to a host of important metatheoretical assumptions.

Good Genes Sexual Selection Theory

In order to adequately characterize the evolution of reproductive strategies, one must consider parental investment theory in conjunction with other middle-level theories of sexual selection. In this section we provide a detailed overview of good genes sexual selection theory, as well as briefly summarize the three other main theories of sexual selection (via direct phenotypic benefits, runaway processes, and sensory bias).

The male long-tailed widowbird, as its name suggests, has an extraordinarily elongated tail. Although the body of this EastAfrican bird is comparable in size to that of a sparrow, the male’s tail feathers stretch to a length of up to 1.5 meters during the mating season. These lengthy tail feathers do little to enhance the male widowbird’s survival prospects: They do not aid in flight, foraging, or defense from predators. Indeed, having to haul around such a tail is likely to reduce survival prospects through increased metabolic expenditure, attraction of predators, and the like. The question that has to be asked of the male widowbird’s tail is how it could possibly have evolved. The short answer is that female widow birds prefer males with such exaggerated traits—that is, the male widowbird’s extraordinary tail has evolved by the process of sexual selection. That such a female preference for long tails exists was confirmed in an ingenious manipulation experiment carried out by Malte Andersson (1982). In this study, some males had their tail feathers experimentally reduced while others had their tails enhanced.The number of nests in the territories of the males with the supernormal tails significantly exceeded the number of nests in the territories of those males whose tails had been shortened. Clearly female widowbirds preferred to mate with males who possess the superlong tails.

To explain why the female widowbird’s preference for long tails has evolved, we need to consider the various mechanisms and theories of sexual selection. The two main mechanisms of sexual selection that have been identified are mate choice (usually, but not always, by females) and contests (usually, but not always, between males). The male widowbird’s elongated tail is an example of a trait that has apparently evolved via female choice. The 2.5-m tusk of the male narwhal, by contrast, is a trait that appears to have evolved in the context of male-male competition. Other, less studied mechanisms of sexual selection include scrambles for mates, sexual coercion, endurance rivalry, and sperm competition (Andersson, 1994; Andersson & Iwasa, 1996). In his exhaustive review of sexual selection in over 180 species, Andersson (1994) documents evidence of female choice in 167 studies, male choice in 30 studies, male competition in 58 studies, and other mechanisms in 15 studies. Sexual selection, as illustrated in a recent book by Geoffrey Miller (2000), has also been proposed as an important mechanism for fashioning many traits in our own species, including such characteristics as music, art, language, and humor.

Four main theories about how sexual selection operates have been advanced: via good genes, direct phenotypic benefits, runaway processes, and sensory bias. These different theories, however, are not necessarily mutually exclusive and may be used together to explain the evolution of sexually selected traits. The core idea of good genes sexual selection is that the outcome of mate choice and intrasexual competition will be determined by traits that indicate high genetic viability (Andersson, 1994; Williams, 1966). Males (and, to a lesser extent, females) of many bird species, for example, possess a bewildering variety of ornaments in the form of wattles, plumes, tufts, combs, inflatable pouches, elongated tail feathers, and the like. Moreover, many male birds are often splendidly attired in a dazzling array of colors: iridescent blues, greens, reds, and yellows. Keeping such elaborate visual ornamentation in good condition is no easy task. It requires time, effort, and—critically—good health to maintain. Females who consistently choose the brightest, most ornamented males are likely to be choosing mates who are in the best condition, which reflects the males’ underlying genetic quality. Even if females receive nothing more than sperm from their mates, they are likely to have healthier, more viable, and more attractive offspring if they mate with the best quality males. According to Hamilton and Zuk (1982), bright plumage and elaborate secondary sexual characteristics, such as the male peacock’s resplendent tail, are accurate indicators of the relative parasite loads of different males. A heavy parasite load signals a less viable immune system and is reflected in the condition of such traits as long tail feathers and bright plumage.

Many secondary sexual characteristics therefore act as indicators of genetic quality. Moreover, according to the handicap principle developed by Amotz Zahavi (1975; Zahavi & Zahavi, 1997), such traits must be costly to produce if they are to act as reliable indicators of genetic worth. If a trait is not expensive to produce, then it cannot serve as the basis for good genes sexual selection because it will not accurately reflect the condition of its owner. However, if the trait relies on substantial investment of metabolic resources to develop—as does the male widowbird’s tail—then only those individuals in the best condition will be able to produce the largest or brightest ornament. In this case, expression of the trait will accurately reflect underlying condition.

In a slightly different take on the handicap principle, Folstad and Karter (1992) have suggested that in males, high levels of testosterone, which are necessary for the expression of secondary sexual characteristics (those sex-linked traits that are the product of sexual selection), also have harmful effects on the immune system. According to this immunocompetence handicap model, only the fittest males will be able to develop robust secondary sexual characteristics, which accurately indicate both high levels of testosterone and a competent immune system—and therefore high genetic quality. These general hypotheses were supported in a recent metaanalysis of studies on parasite-mediated sexual selection. This meta-analysis demonstrated a strong negative relationship between parasite load and the expression of male secondary sexual characteristics. In total, the most extravagantly ornamented individuals are also the healthiest ones—and thus the most preferred as mates (Moller, Christie, & Lux, 1999). Of course in species in which there is substantial paternal investment (including humans), males will also be choosy about whom they mate with and will also select mates with indicators of high genetic fitness. In many bird species, for example, both males and females are brightly colored or engage in complex courtship dances. Thus, relative levels of parental investment by males and females substantially influence the dynamics of good genes sexual selection.

Genes, of course, are not the only resources that are transferred from one mate to another in sexually reproducing species.Although the male long-tailed widowbird contributes nothing but his sperm to future offspring, in many species parental investment by both sexes can be substantial. It benefits each sex, therefore, to attend to the various resources that mates contribute to subsequent offspring; thus, one of the driving forces behind sexual selection is the direct phenotypic benefits that can be obtained from mates and mating. These benefits encompass many levels and types of investment— from the small nuptial gifts offered by many male insect species to the long-term care and provisioning of offspring.

Homo sapiens is a species commonly characterized by long-term pair-bonding and biparental care of offspring. Therefore, in addition to traits that indicate the presence of good genes, both males and females should be attentive to characteristics that signal the ability and willingness of potential mates to devote time and external resources to future offspring. As has been demonstrated in many studies of human mate preferences (see Buss, 1994), both males and females rate kindness and warmth as the most important attributes in long-term mates.Apartner with the personality traits of kindness, honesty, and warmth is someone who is both more likely to remain in a long-term relationship and who will invest time and resources in future offspring. Women (more so than men) also rate the presence of status and resource-accruing potential as important attributes in potential mates (Buss, 1989), suggesting that males with the ability to contribute external resources to future offspring are favored.

It is important to note that some characteristics may be indicative of both good genes and the ability to offer direct phenotypic benefits; thus, these two different theories of sexual selection are not necessarily incompatible. For example, a male bird with bright, glossy plumage may be preferred as a mate not only because of his high genetic quality, but also because he is less likely to transmit parasites to prospective sexual partners. However, compatibility between good genes and direct benefits is often not apparent, and it is expected that the relative importance of these two mate selection criteria will vary on a species-by-species basis. We also expect variation to occur within species in the relative weighting of good genes versus direct phenotypic benefits in mate selection (Gangestad & Simpson, 2000; Gross, 1996). For example, Gangestad and Simpson (2000) have argued that human females make trade-offs between males with traits indicating good genes and males with traits signaling high likelihood of paternal investment. Some women at some times pursue a relatively unrestricted strategy of engaging in short-term sexual relationships with partners who may be high in genetic quality, whereas other women may adopt a more restricted strategy of selecting long-term partners who are likely to offer substantial paternal investment. The prevalence of extrapair mating in humans suggests that both strategies may be pursued simultaneously: Resources may be extracted from one high-investing male while extrapair matings are pursued with other males who display indicators of high genetic quality (see earlier discussion of the function of female orgasm). Men also must make trade-offs between seeking multiple sexual partners and investing substantially in only one or a few mates. Which strategies are chosen is determined in part by such factors as father absence, individual differences in mate value, and availability of mates (e.g., Draper & Harpending, 1982; Gangestad & Simpson, 2000; Kirkpatrick & Ellis, 2001).

So far we have discussed good genes and direct phenotypic benefits as ways of understanding the dynamics of sexual selection. Two other processes have also been suggested that can account for the evolution of sexually selected traits. The first of these theories— runaway sexual selection (Fisher, 1958)—states that preferences and traits coevolve through a feedback process that can lead to the rapid evolution of specific traits for essentially arbitrary reasons. For example, consider that females of given lizard species have a preference for males with an enlarged and elaborate head crest. This preference may have evolved initially because such males may have greater genetic viability (i.e., good genes) or because of some innate sensory bias (discussed further later in this research paper). Males with the enlarged crests will become more prevalent in the population and the female preference for the trait will also become more widespread. Males with large crests increase their inclusive fitness by enhanced mating opportunities and females advance their inclusive fitness because they are more likely to have male offspring with the enlarged crest, who will in turn be more likely to succeed in mating contexts. After the preference is in place, however, the elaborate crest may become decoupled from any indicator of health or fitness and simply spread because of the preference per se. The male crest will increase in size as the trait and the preference for the trait coevolve until the crest becomes so large and elaborate that it undermines survival.

Unlike good genes sexual selection, empirical evidence for the runaway process (in its pure form) is fairly sparse. However, Eberhard (1985, 1993) has suggested that the evolution of male genitalia may prove an instructive example of runaway sexual selection in action. As documented in Eberhard’s fascinating book, Sexual Selection and Animal Genitalia, male genitalia come in a bewildering variety of shapes and sizes—they are often decorated with knobs, spines, hooks, and flanges that are seemingly unrelated to the utilitarian task of sperm transfer. Eberhard (1993) argues that it is un likely that variations in penis morphology are useful indicators of the ability to resist parasites or of general male vigor (i.e., they are probably not reliable markers of good genes). It seems plausible instead to suggest that female preferences, due initially to biases towards certain kinds of tactile stimulation, have coevolved with genitalia morphology in classic runaway fashion, leading to the seemingly arbitrary array of genitalia structures found in the animal world.

A key aspect of the runaway process is that traits that are preferred are arbitrarily related to fitness in the sense that such traits do not indicate genetic viability (as is the case with good genes models). However, the runaway process has to begin with a preference that is usually based on actual viability or is the result of sensory bias. The sensory bias model of sexual selection involves the evolution of traits via sexual selection due to preferences resulting from sensory orientations that are the product of other selective processes (Ryan & Keddy-Hector, 1992). Whereas in good genes and runaway sexual selection, preferences and traits coevolve, the sensory bias theory requires the prior origin of preferences and the latter evolution of traits that exploit those preferences. The evolution of male calls of the Tungara frog appears to be explained by this sensory-bias model of sexual selection. Females prefer male frogs with low-frequency calls. Neurophysiological evidence indicates that the auditory system of female frogs is tuned in a way that is biased toward the low-frequency component of these calls. Because bigger male frogs produce lower-frequency calls, a good genes model of sexual selection may seem indicated. However, Ryan and Rand (1990) argue that because closely related frog species also demonstrate this female bias in the absence of male calling, the male trait arose to exploit the preexisting sensory bias of the females, which itself has arisen as the result of other selective forces.

Good genes sexual selection is another important middlelevel theory that has proven valuable in generating a number of interesting and testable hypotheses about both human and nonhuman animal behavior. As we have discussed, good genes sexual selection theory is one of a number of alternative (although often compatible) middle-level theories of sexual selection. Making predictions that distinguish between these different middle-level applications of sexual selection metatheory can sometimes be difficult. However, as reviewed in the next section, good genes sexual selection theory (often in conjunction with parental investment theory) enables us to derive a number of general hypotheses and specific predictions that can be empirically tested.

The Hypotheses Level of Analysis

At the next level down in the hierarchy of explanation are the actual hypotheses drawn from middle-level evolutionary theories (see Figure 1.1). As noted earlier, a hypothesis is a general statement about the state of the world that one would expect to observe if the theory from which it was generated were in fact true.An array of hypotheses can often be derived from a single middle-level theory. These hypotheses can be considered to vary along a continuum of confidence (Ellis & Symons, 1990). At the top of the continuum are socalled firm hypotheses (such as the relation between relative parental investment and intrasexual competition for mating opportunities) that are clear and unambiguous derivations from an established middle-level evolutionary theory. As one moves down the continuum, however, firm hypotheses give way to more typical formulations—hypotheses that are inferred from a middle-level theory but not directly derived from it. This distinction can be illustrated by considering the issue of paternity uncertainty. The supposition that in species characterized by both internal female fertilization and substantial male parental investment, selection will favor the evolution of male mechanisms for reducing the probability of expending that investment on unrelated young is a firm hypothesis that can be directly derived from the theory. What form these mechanisms will take, however, cannot be directly derived from the theory because natural and sexual selection underdetermine specific evolutionary paths. Selection could favor the evolution of sexual jealousy, or it could favor the evolution of sperm plugs to block the cervix of female sexual partners following copulation (see earlier discussion of mate retention strategies). Given the universal occurrence of jealousy in humans (Daly et al., 1982), evolutionary psychologists have hypothesized that men’s jealousy should be centrally triggered by cues to sexual infidelity, whereas women’s jealousy should be centrally triggered by cues to loss of commitment and investment. This hypothesis is reasonably inferred from the theory but cannot be directly deduced from it. We refer to this type of hypothesis as an expectation. This hypothesis was originally proposed by Daly et al. (1982) and has since received considerable empirical support (Buss, Larsen, Westen, & Semmelroth, 1992; Buunk, Angleitner, Oubaid, & Buss, 1996; DeSteno & Salovey, 1996; Wiederman & Allgeier, 1993).

As one moves farther down the continuum of confidence into the area where inferences from middle-level theories are drawn farther from their core, expectations grade insensibly into interesting questions or hunches. At this level, different interpretations of the theory can and do generate different hypotheses. For example, Buss and Shackelford (1997) have proposed two competing evolutionary hypotheses concerning the effects of unequal attractiveness between romantic partners on women’s mate retention behavior. The first hypothesis suggests that individuals (both women and men) married to others who are perceived as more attractive than the self will devote more effort to mate retention than will individuals married to others who are perceived as equally or less attractive than the self. The logic behind this hypothesis is that individuals who are married to relatively attractive partners are at greater risk of losing them. The second hypothesis suggests the opposite, but only for females: Women married to men who are perceived as more attractive than the self will relax their mate retention efforts. The logic behind this hypothesis focuses on the greater ability of men to fractionate their reproductive investment among multiple partners. For example, a man can simultaneously beget and raise children with three different women (a phenomenon that is quite common in polygynous societies), whereas it would take a woman several years to bear and raise children with three different men. Because of the male ability to partition investment, women may face the trade-off of obtaining a fraction of the attention and resources of a highly attractive male or the full attention and resources of a less attractive male. Buss and Shackelford (1997) suggest that women in unevenly matched marriages might devote less effort to mate retention, an implicit acknowledgment of the potential costs involved in trying to prevent the more attractive partner from devoting some of his resources to outside relationships.

Although this type of theorizing is admittedly speculative, it is inevitable at the lower end of the continuum of confidence—in domains where there is not strong middlelevel theoretical development and about which relatively little is known. Studies designed to test these hypotheses often have an exploratory quality. The data obtained from testing such hypotheses, however, can work their way back up the explanatory hierarchy to enable the development of more rigorous theoretical models (Ketelaar & Ellis, 2000). In the following section, we review hypotheses derived from good genes sexual selection theory. We number these hypotheses and note whether (in our opinion) they are firm hypotheses, expectations, or hunches.

Good Genes Sexual Selection Theory: Hypotheses

The principles of good genes sexual selection theory in combination with parental investment theory have been used to generate a number of interesting hypotheses in a variety of species, including humans. In the following discussion we use the term females to refer to the sex that invests more in offspring and males to refer to the sex that invests less in offspring. We recognize, of course, that these sex roles are sometimes reversed.

For a given trait to be a reliable indicator of genetic value, it must be costly to produce. According to the handicap principle (Zahavi & Zahavi, 1997), traits that indicate good genes can only be maintained by individuals who are the fittest in the population, as indicated by their ability to maintain steady growth rates, resist parasites, compete successfully in intrasexual contests, and so forth. Consequently, good genes indicators that are preferred by members of the opposite sex should require substantial metabolic resources to develop and maintain. It follows, therefore, that individuals who more fully display traits indicative of high genetic quality should be healthier and in better condition than should conspecifics who display these traits less fully (H1; firm hypothesis). An implication of this hypothesis is that individuals with elaborate secondary sexual characteristics should have lower levels of parasitic infection. Further, traits indicative of good genes can only be developed to their fullest potential in individuals with robust immune systems that are able to overcome the immunosuppressant effects of sex hormones such as testosterone (see earlier discussion of immunocompetence handicap theory; Folstad & Karter, 1992). Expression of traits indicative of good genes, therefore, should be positively related to effective immune system functioning.

Evidence that sexually selected traits can increase reproductive success while reducing survival prospects (i.e., handicap traits) has accumulated in a number of species, including the European barn swallow. The male barn swallow is adorned with elongated tail feathers. Males with longer tail feathers are preferred by females and sire more offspring (Moller, 1994). However, males with such long tails are less efficient at foraging and are more likely to suffer predation by birds of prey (Moller et al., 1998). Thus, female preference for males with elongated tail feathers appears to reflect good genes sexual selection in action. A recent meta-analysis of studies assessing parasite load, immune function, and the expression of secondary sexual characteristics in a diverse array of species has found that the fullest expression of sexually selected traits is positively related to immune system functioning and negatively related to parasite load (Moller et al., 1999)—that is, the brightest, largest, most ornamented individuals are also the ones with the smaller number of parasites and the most robust immune systems.

An important factor influencing the intensity of good genes sexual selection is variance in reproductive success. Two principles are relevant here. First, there tends to be greater variance in male than in female reproductive success; this is because males are more able to distribute their sex cells across multiple partners. Indeed, the ability of males to inseminate a large number of females often results in a sexual lottery in which some males win big while others lose out entirely. For example, in one study of elephant seals, a total of only eight males were found to be responsible for inseminating 348 females (Le Boeuf & Reiter, 1988). Second, because of this disparity, sexual selection tends to act more strongly on males than on females in shaping intrasexual competitive abilities and producing specialized fitness signals for attracting the opposite sex (Trivers, 1972; see also Cronin, 1991).

A core premise of good genes sexual selection is that certain traits have evolved because they are reliable indicators of genetic quality—that is, these traits reliably signal viability and good condition that can be passed on to offspring through genetic inheritance. All else being equal, individuals that possess such traits should be preferred as mates (H2; firm hypothesis), be more successful in intrasexual contests (H3; firm hypothesis), or both. Parental investment theory further suggests that males will be more likely than females to possess and display indicators of genetic quality (H4; expectation), whereas females will be more likely than males to select mates on the basis of these indicators (H5; expectation). In total, then, males that possess and display indicators of genetic quality should have more sexual partners and more offspring (H6; firm hypothesis). For example, among mandrills, a primate that inhabits the rainforests of West Africa, males who possess the brightest red and blue pigmentation on the face, rump, and genitals (which presumably are indicators of good genes) are more often preferred as mates by females. Further, DNA analysis has shown that they are also more likely than their less chromatically exuberant counterparts to sire offspring (Dixson, Bossi, & Wickings, 1993).

In species in which females engage in nonreproductive, situation-dependent sexual activity (rather than strictly cyclical sexual activity), females’ preferences for males who display indicators of high genetic quality should vary as a function of their phase of the reproductive cycle. Around the time of ovulation, when females are most fertile, they should express the strongest preference for males with good genes.At other times in the reproductive cycle, when females are not ovulating, this preference should be more muted (H7; expectation). Humans are the clearest example of a primate that engages in sexual activity throughout the reproductive cycle. Other primates tend to be more seasonal and cyclical in their breeding activities than humans are, although not exclusively so (see Hrdy, 1981).

We earlier discussed the selective sperm retention hypothesis for female orgasm, which suggests that females exert some control over the paternity of their offspring by differential patterns of orgasm with specific male partners. In species characterized by female orgasm, the frequency and timing of female orgasm should vary in a manner that selectively favors the sperm of males who display indicators of high genetic quality (H8; hunch).

Good genes sexual selection theory has been used to generate hypotheses about mating effort, parental effort, and trade-offs between them. There are essentially three strategies that individuals can use to increase their reproductive success: (a) Increase the fitness of their offspring by mating with individuals of high genetic quality, (b) increase the fitness of their offspring by enhancing parental investment (by one or both parents), or (c) increase the number of offspring produced. No one strategy is inherently better than any other, and the pursuit of one strategy usually involves trade-offs with the others (see Gangestad & Simpson, 2000). For example, individuals who produce a greater number of offspring (c) tend to have lower fitness of offspring.

Consistent with (a), females can increase their reproductive success by preferentially investing in offspring that are sired by males of high genetic quality. Thus, among females there should be a positive correlation between levels of parental investment in offspring and the genetic quality of the offspring’s father (H9; expectation). Peahens, for example, have been found to lay more eggs for peacocks with larger trains and more elaborate tails (Petrie & Williams, 1993).

In species characterized by long-term pair-bonding and biparental care of offspring, but in which individuals sometimes engage in short-term and extrapair mating, there should be a negative correlation between the genetic quality of males and levels of parental investment by males in offspring (H10; expectation). There are two bases for this hypothesis. First, males who possess reliable indicators of high genetic quality can afford to put less direct effort into offspring; this is because they make more valuable genetic contributions to offspring, and thus their female partners may be willing to tolerate less parental investment—devaluing (b)—in return for their good genes—enhancing (a). Second, diverting effort away from parental investment toward extrapair matings should yield greater payoffs for males of high genetic quality (because they are more popular on the mating market). Thus, males with good genes can be expected to devote proportionally more reproductive effort to mating (c) and less to parenting (b). A corollary of this hypothesis is that males who possess reliable indicators of good genes will engage in more short-term and extrapair mating (H11; expectation) and be more preferred by females as short-term and extrapair mates (H12; expectation).

Hypotheses 10–12 have been supported in an extensive series of studies on the European barn swallow. The barn swallow is small, migratory, insect-eating bird, which is characterized by pair-bonds that last the length of the breeding season and biparental care of offspring. Male and female birds are similar in many respects except that males have much longer tails than do females, which suggests that tail length is a sexually selected characteristic (Moller, 1994). Males with longer tail feathers not only tend to spend less time incubating and feeding offspring (Moller, 1994), but also are more preferred by females as primary mates, engage in more extrapair mating, and sire more extrapair offspring than do males with shorter tails (Moller & Tegelstrom, 1997). These data suggest that (a) females are willing to trade off parental investment for good genes in their primary pairbonds and (b) females pursue extrapair copulations with males who possess indicators of good genes. We find it interesting that the probability of females’ pursuing extrapair copulations decreases as a function of the length of the tail feathers of their primary mate (Moller, 1994), suggesting females who are already receiving high-quality genetic benefits have less motivation for extrapair mating.

In sum, hypotheses derived from good genes sexual selection theory can explain the origins of a wide variety of physical and behavioral traits across a diversity of animal species, from humans to scorpion flies. The specific ways in which these hypotheses are played out, however, depends on the nature of the species being studied. Humans and barn swallows, for example, both engage in medium- to long-term pairbonding, both have greater female parental investment, and both are characterized by relatively frequent extrapair mating. We would expect, therefore, that females in both species will preferentially seek extrapair sex partners who possess indicators of good genes. However, specific markers of good genes vary across species. Human males do not possess elongated tail feathers, bright spots on their rump, or bright red faces. Thus, although the general hypotheses derived from good genes sexual selection theory have wide applicability, the detailed predictions derived from these hypotheses depend on the species under consideration. In the next section we describe specific predictions as they apply to human mating.

The Prediction Level of Analysis

Because hypotheses are often too general to be tested directly, it is at the next level of explanation—the level of specific predictions—where the battles between competing theoretical models are often played out. Predictions correspond to specific statements about the state of the world that one would expect to observe if the hypothesis were in fact true. They represent explicit, testable instantiations of hypotheses. One might argue that predictions form the substance of any theory, for here is where most of the action takes place as specific predictions are either supported or refuted.

The performance of evolution-based predictions provides the basis for evaluating the more general hypotheses from which they are drawn. For example, a number of specific predictions have been derived from the evolutionary hypothesis that men (more than women) will be intensely concerned about the sexual fidelity of reproductive-aged partners. Some of these predictions include (a) sexual infidelity by wives will be a more frequent cause of divorce than will sexual infidelity by husbands (Betzig, 1989); (b) the use or threat of violence by husbands to achieve sexual exclusivity and control of wives will vary as a function of wives’ reproductive value, which peaks in the late teens and declines monotonically thereafter (M. Wilson & Daly, 1996); and (c) in the context of competing for romantic partners, the tactic of spreading rumors that a same-sex rival is sexually promiscuous will be more effective when performed by women than by men (because it raises the specter of cuckoldry; see Buss & Dedden, 1990). The fact that the first two predictions have been supported by extensive cross-cultural data whereas the third prediction has not been supported factors into one’s evaluation of the more general hypothesis from which these predictions were generated. That two of the three predictions garnered strong support provides indirect support for the hypothesis. That the third prediction was rejected raises questions about the hypothesis. Ultimately, the value of the more general hypothesis and theoretical model is judged by the cumulative weight of the evidence (Ketelaar & Ellis, 2000).

Good Genes Sexual Selection Theory: Predictions

A number of specific, testable predictions can be derived from the hypotheses generated by good genes sexual selection theory. Although predictions can be made about the characteristics of a wide array of animal species, we focus in this section on a discussion of predictions pertaining specifically to humans. We consider the hypotheses outlined in the preceding section (“The Hypothesis Level of Analysis”) and derive predictions relating specifically to human health and reproductive behavior. For each prediction we also review studies, where relevant, that have been carried out to test these specific predictions.

Before we examine these predictions in detail, it is worth considering just what traits in humans—like elongated tail feathers in male barn swallows—might be reliable indicators of good genes. One important marker of genetic quality that has emerged in research on a diverse array of species is a phenomenon known as fluctuating asymmetry (Moller & Swaddle, 1997). Fluctuating asymmetry refers to small random deviations from perfect bilateral symmetry in different parts of the body. Higher levels of fluctuating asymmetry (i.e., more asymmetry) are believed to reflect developmental instability. This developmental imprecision can arise because of a range of factors, such as food deficiency, parasites, inbreeding, and exposure to toxic chemicals. Biologists have hypothesized that individuals with good genes are better able to buffer themselves against these genetic and environmental insults and thus tend to be more symmetrical. Because fluctuating asymmetry has a heritable component, mate preference for symmetrical, developmentally stable individuals can be expected to result in more viable offspring (see Moller & Swaddle, 1997). The specific predictions reviewed in this section focus on the relations between fluctuating asymmetry and both health and reproductive behavior.

  • More symmetrical individuals should have better mental and physical health, better immune system functioning, and lower parasite loads than should less symmetrical individuals (from H1). Although these predictions have only been tested in a small number of studies using human participants, initial results have been largely supportive. In studies of American undergraduates, levels of symmetry in both men and women have been found to positively correlate with psychometric intelligence (Furlow, Armijo-Prewitt, Gangestad, & Thornhill, 1997) and negatively correlate with measures of psychological, emotional, and physiological distress (Shackelford & Larsen, 1997). In addition, more symmetrical men have been found to have greater ejaculate size and better sperm quality (Manning, Scutt, & Lewis-Jones, 1998) and lower resting metabolic rates (Manning, Koukourakis, & Brodie, 1997) than have less symmetrical men. Perceived health has also been shown to be positively correlated with symmetry and averageness of male faces (Rhodes et al., 2001). Finally, in a study of men in rural Belize, the occurrence of life-threatening illnesses was found to be significantly higher in men who were less symmetrical (Waynforth, 1998). Taken together, these findings suggest that more symmetrical individuals, as predicted, tend to be healthier and in better physical and psychological condition than do their less symmetrical counterparts.

The remaining hypotheses (H2–H12) focus on the relations between markers of genetic fitness and reproductive behavior. Because of sex differences in parental investment, these hypotheses primarily concern female preferences for males who possess indicators of good genes and individual differences in male mating behavior as a function of genetic quality. An array of specific predictions have been derived from Hypotheses 2–12. As reviewed in the following discussion, empirical tests of these predictions have generated new lines of research that have substantially advanced our understanding of behavior in sexual and romantic relationships.

  • More symmetrical men should have more lifetime sexual partners (from H2–H6) and more extrapair sexual partners (from H10) than should less symmetrical men. These predictions have been tested in an initial series of studies on American undergraduates (reviewed in Gangestad & Simpson, 2000; Gangestad & Thornhill, 1997a). Symmetry was assessed by totaling right-left differences in seven bilateral traits (e.g., ankle girth, wrist girth). Consistent with the predictions, men who were more symmetrical were found to have more lifetime sexual partners (even after controlling for age and physical attractiveness) and more extrapair sexual encounters during ongoing relationships (even after controlling for relationship length, partners’ extrapair sex, and both partners’ physical attractiveness). In contrast, no consistent relation was found between women’s symmetry and number of lifetime sexual partners or extrapair sexual relationships.

In ancestral environments, before the advent of reliable contraceptive methods, number of sexual partners can be expected to have been positively related to number of offspring. The finding that more symmetrical men in rural Belize both had more sexual partners and fathered more children lends support to this suggestion (Waynforth, 1998).

  • More symmetrical men should be more successful inintrasexual contests than should less symmetrical men (from H2, H4). This prediction has been tested both indirectly (by looking at the traits associated with fluctuating asymmetry) and directly (by examining behavior in experimental studies on mate competition). Men who are more symmetrical have been found to display higher levels of traits that are associated with success in intrasexual competition. Specifically, more symmetrical men tend to be bigger, to be more muscular and vigorous, to initiate more fights with other men, and to be more socially dominant than do less symmetrical men (reviewed in Gangestad & Simpson, 2000). Consistent with these correlational data, Simpson, Gangestad, Christensen, and Leck (1999) found that more symmetrical men competed more aggressively with other men for a lunch date with an attractive woman in a laboratory experiment. Each male participant was interviewed by the woman and then at the end of the interview was asked by the woman why she should choose him for the lunch date rather than the competitor (who was ostensibly in the next room). Compared with men who were less symmetrical, more symmetrical men tended to engage in competition with the rival, such as by directly comparing themselves with and belittling him. In total, the correlational and experimental data reviewed here suggest that more symmetrical men tend to display more costly traits, such as large size and social and physical dominance, which facilitate success in direct intrasexual contests.
  • More symmetrical men should be preferred by womenas short-term and extrapair sexual partners (from H11). Gangestad, Simpson, Cousins, and Christensen (1998) had women view videotapes of men being interviewed by an attractive woman (as described previously). The female participants then rated the male interviewee’s attractiveness both as a potential long-term mate and as a short-term mate. A shortterm mate was defined as either as a one-time sex partner or an extrapair sex partner. Women also completed a questionnaire that assessed their general willingness to have sex without commitment and emotional closeness. Women who reported more willingness to have sex without intimacy and commitment were categorized as being inclined toward short-term mating, whereas women who reported less willingness were categorized as being disinclined toward shortterm mating. Among women who were inclined toward short-term mating, there was a significant positive correlation between the male interviewee’s symmetry and the women’s ratings of how attractive he was as a short-term mate (but not as a long-term mate). In contrast, among women who were disinclined toward short-term mating, male symmetry was uncorrelated with women’s ratings of how attractive he was as either a short-term or a long-term mate. These data suggest that men who are more symmetrical are preferred as shortterm mates specifically by women who are most inclined to engage in short-term mating. Moreover, Gangestad and Thornhill (1997b) found that male symmetry predicted the number of times that men were chosen by women as extrapair mates. Taken together, these data support the prediction that more symmetrical men should be more preferred by women as short-term and extrapair sexual partners.
  • Women’s preferences for symmetrical men should beheightenedaroundthetimeofovulationwhenwomenaremost fertile (from H7). This prediction has been supported in provocativenewresearchonwomen’spreferenceforthescent of symmetrical men as a function of variation in the menstrual cycle. This research employed what has been called a stinky T-shirt design, in which women sniffed shirts that had been slept in by different men and rated them on the pleasantness, sexiness, and intensity of their odors. The men who slept in theseshirtswerealsomeasuredonfluctuatingasymmetry.The extraordinary finding was that the shirts worn by more symmetricalmenwereratedassmellingbetterthantheshirtsworn by less symmetrical men, but only by women who were likely to be in the fertile stage of their menstrual cycle (especially days6–14).ThisfindingwasoriginallyreportedbyGangestad and Thornhill (1998a) and has since been replicated in their own lab in the United States (Thornhill & Gangestad, 1999) andinanindependentlabinGermany(Rikowski&Grammar, 1999). These data suggest that the smell of men who are more symmetrical is preferred by women specifically when women are most likely to conceive.
  • Women’s preferences for men with masculine facialcharacteristics should be heightened around the time of ovulation when women are most fertile (from H7). As discussed earlier, the immunocompetence handicap model suggests that only the fittest males will be able to develop robust secondary sexual characteristics, which accurately indicate both high levels of testosterone and a competent immune system (i.e., good genes). Exaggerated masculine facial characteristics, such as high cheekbones and a strong jaw and chin, are associated with high levels of testosterone and have been hypothesized to be reliable indicators of immunocompetence in men (see Folstad & Karter, 1992). Recent research in the United Kingdom and Japan has examined variation in women’s preferences for male faces as a function of women’s stage in the menstrual cycle (Penton-Voak et al., 1999; Penton-Voak & Perrett, 2000). Consistent with good genes sexual selection theory, more masculine-looking faces were preferred by women around the time of ovulation (when risk of conception is highest), especially in the context of short-term mating. In contrast, more feminine male faces, which may indicate dispositions toward increased paternal investment, were slightly preferred by women during other phases of the menstrual cycle (when risk of conception is lower). These data provide further evidence that men who display indicators of good genes are most preferred by women when they are most likely to get pregnant.
  • The timing and frequency of orgasms by women shouldbe patterned to selectively retain the sperm of more symmetrical males (from H8). Thornhill et al. (1995) have conducted an initial test of this prediction on a sample of American undergraduates. The partners of more symmetrical men reported having more orgasms during sexual intercourse than did the partners of less symmetrical men (even after controlling for men’s physical attractiveness). More important, levels of symmetry in male partners positively correlated with the frequency of high-sperm-retention orgasms in female partners (i.e., female orgasms occurring just prior to or after male orgasm). This effect has now been replicated in a second larger sample (Moller, Gangestad, & Thornhill, 1999). These data suggest that women increase their probability of conception when having sex with men of high genetic quality.
  • More symmetrical men should allocate less investmentto ongoing relationships (from H10). Using the PartnerSpecific Investment Inventory (Ellis, 1998), Gangestad and Thornhill (1998b) examined levels and types of investment in long-term dating relationships. More symmetrical men, who tended to allocate less investment to their dating relationships overall, were particularly likely to be less honest with their partners, to sexualize other women more, and to spend less time with their partners. The exception to this rule was that more symmetrical men tended to provide more physical protection to their partners. Although symmetrical men apparently devote less time and energy to their relationships overall, they may compensate (reproductively speaking) for this lack of investment by providing good genes and perhaps through their greater ability to physically protect their partners.

In conclusion, specific predictions drawn from hypotheses generated by good genes sexual selection theory have been tested across a range of studies. Although research derived from good genes sexual selection theory on humans is still in its early stages, an accumulating body of evidence now supports the supposition that a collection of male traits (reflected in levels of fluctuating asymmetry) have been selected for because of their role in advertising genetic quality to prospective mates. Good genes sexual selection theory has proven valuable in guiding research in a number of ways and has led to the detection of new phenomena. It is difficult imagine, for example, how other approaches to human mating could have predicted (let alone explained) the finding that men’s symmetry is positively related to judgments of odor attractiveness by women who are most likely to be in the fertile stage of their menstrual cycle. Of course, there is much more to the dynamics of sexual and romantic relationships than can be explained by good genes sexual selection theory. This middle-level evolutionary theory has proved valuable, however, in both explaining and predicting a host of interesting phenomena relating to behavior in sexual and romantic relationships—not only in humans, but also in a wide range of animal species.

The Future of Evolutionary Psychology

Evolutionary explanations have had a long—at times acrimonious—history in the behavioral sciences. Darwin’s revolutionary theory of adaptation through natural selection, which explained the origins of human mental and behavioral characteristics in terms of evolution, transformed a long-standing worldview. Before Darwin, the prevailing belief was that “man” was created in God’s divine image and held a special place at the center of the cosmos. Ever since Darwin, however, Homo sapiens has been viewed as firmly anchored in the natural world, as one species among millions in the great tree of life.

Darwin himself saw no problem in extrapolating his evolutionary ideas beyond the realm of bees, barnacles, and baboons to embrace the human species as well (e.g., Darwin, 1871, 1872). Others too, such as Darwin’s protégé George Romanes (1882), appreciated the great explanatory power of evolutionary theory. Romanes used it to launch a comparative program of research aimed at illuminating the evolutionary origins of human intelligence. In America, the great nineteenth-century psychologist and philosopher William James (1890) also characterized human consciousness in a Darwinian fashion as a mechanism that enables humans to adapt to changing environments. James’s evolution-inspired ideas were to spark the short-lived but influential functionalist movement in psychology in the early part of the twentieth century. The core idea of functionalism was that mind and behavior have functions —they serve to adapt organisms to their environment (e.g., Angell, 1907). Functionalist thinking in psychology, however, fell out of favor with the rise of behaviorism in the early part of the twentieth century. The behaviorist paradigm, which specified that a small number of domain-general learning mechanisms accounted for the rich repertoire of human (and animal) behavior, precluded an explanatory role for the kinds of species-specific, domainspecific psychological mechanisms that are central to functionalist, evolutionary analyses.

The return of evolutionary explanations in psychology can be traced to a number of important developments. First, behaviorism declined as psychology’s dominant paradigm. Animal behavior research in the 1950s and 1960s demonstrated that the content-free learning processes specified by behaviorists simply could not account for the kinds of behaviors in which animals actually engaged (e.g., Breland & Breland, 1961; Garcia & Koelling, 1966). Behaviorism in its pure form also seemed unable to satisfactorily explain the origin of complex human traits such as language, which linguists such as Chomsky (1959) argued were built on a foundation of innate cognitive processes. Second, the development of a number of important middle-level evolutionary theories in the 1960s and 1970s, such as kin selection theory (Hamilton, 1964), parental investment theory (Trivers, 1972), and reciprocal altruism (Trivers, 1971) provided the basis for important new programs of research in evolutionary biology and psychology. These middle-level theories enabled evolutionary scientists to generate myriad testable hypotheses and predictions that spanned a diversity of animal species.

The formulation of these middle-level theories was important in the emergence in the late 1970s of sociobiology, which was defined by one of its principle architects, E. O. Wilson (1975), as “the systematic study of the biological basis of all social behavior” (p. 3). However, sociobiology proved to be a highly controversial discipline, especially when its adherents extended their ideas to explanations of human mental and behavioral characteristics. Sociobiological explanations were variously criticized as being untestable, unfalsifiable, deterministic, and ideologically unsound (e.g., S. Rose, Kamin, & Lewontin, 1984). Evolutionary psychology, as we have introduced it in this research paper, can be viewed historically as part of a long tradition of attempts to explain human psychological characteristics in evolutionary terms. The use of a coherent and powerful set of middle-level theories, the focus on evolved domain-specific psychological mechanisms, and a commitment to rigorous empirical testing, however, sets evolutionary psychology (in some respects) apart from its predecessors.

Controversy nonetheless remains over evolutionary explanations in psychology. Some critics continue to view evolutionary psychology as supporting a view of human nature that is based on genetic determinism—the idea that specific traits are caused by specific genes with a limited role for environmental factors. A glance at almost any publication by evolutionary psychologists, however, should be enough to see that this criticism is unfounded. It is almost universally agreed that all human traits are the result of the complex and dynamic interplay between genetic and environmental factors. Indeed, no evolutionary psychologist would argue that human behavior is rigidly fixed by virtue of our genetic inheritance; instead, much recent work in evolutionary psychology has emphasized the highly flexible and contingent nature of human psychological adaptations (e.g., Dekay & Buss, 1992; Gangestad & Simpson, 2000).

The criticism that evolutionary explanations are somehow untestable and lacking appropriate empirical rigor is still asserted by some critics of evolutionary psychology. This criticism is also unfounded (see Ketelaar & Ellis, 2000, and Ellis & Ketelaar, 2000, for detailed treatment of the issue of testability of evolutionary explanations). As demonstrated in this research paper, evolutionary psychologists employ a series of well-formulated middle-level theories that generate hypotheses and specific predictions that are testable and open to potential falsification. These empirical tests enable one to evaluate the middle-level evolutionary theories and metatheoretical assumptions from which the hypotheses and predictions are drawn. Despite the fact that human psychological characteristics are the product of evolutionary forces operating in ancestral environments, time machines are not essential methodological tools because modern humans carry around the legacy of ancestral adaptations that can be assessed using standard psychological methods.

The Impact of Evolutionary Psychology

Perhaps one of the most interesting questions regarding the future of evolutionary psychology concerns its scope of influence in the behavioral sciences. There is no question that evolutionary psychology has a broad range of applications. Indeed, evolutionary theory has been used to generate explanations of social behavior in all species, even those that are as yet undiscovered. Although the present paper has focused primarily on reproductive strategies, evolutionary psychological theory and research extends into all major branches of psychology (e.g., Buss, 1999; Gaulin & McBurney, 2000). Will the endeavors of evolutionary psychologists thus serve to unify the currently fragmented discipline of psychology under the umbrella of a single metatheory? Does evolutionary psychology, as some suggest (e.g., Buss, 1995; Tooby & Cosmides, 1992), offer a radical new paradigm for psychological science?

To address this question, it is important to explicate the difference between evolutionary ( ultimate ) and nonevolutionary ( proximate ) explanations. Evolutionary psychological explanations focus on ultimate accounts of human psychological characteristics—that is, they explain why traits such as language or sexual jealousy exist in terms of the functions those traits served in ancestral environments. Nonevolutionary psychological explanations, by contrast, generally focus on how traits work in terms of proximate social, developmental, cognitive, or neural processes. Consider the phenomenon of morning sickness in pregnant women. Anultimate explanation for morning sickness is that it is an adaptation that has evolved because it helps to protect the pregnant woman and the developing fetus from the ingestion of toxic substances (Flaxman & Sherman, 2000; Profet, 1992). Proximate explanations of morning sickness focus on current physiological and psychological processes involved in food aversions duringpregnancy. Proximate explanations address such questions as What are the conditions under which morning sickness occurs, What neural circuits are involved, and What are the chemical changes that underpin increased olfactory sensitivity during the first trimester of pregnancy? Neither type of explanation is inherently better than the other, nor does one preclude the other. Rather, ultimate and proximate explanations are complementary and mutually enriching.

Ultimate and proximate explanations, however, are not independent: They inform and influence each other. Discerning the evolved function of a psychological mechanism, for example, should aid in discovering how the mechanism works—that is, understanding evolved function can generate hypotheses about proximate mechanisms and causation. There are various ways to conceptualize the relation between different theories in science. Using the terminology employed by Thagard (1992), we suggest that it is unlikely that the explanations offered by evolutionary psychologists will entirely replace or supplant nonevolutionary explanations. This is because the two types of explanations target different levels of analysis (ultimate vs. proximate causation). Rather, we suggest that the theories offered by evolutionary psychologists tend to sublate extant proximal theories—that is, evolutionary psychological theories partly incorporate and partly reject such theories. Along these lines, we suggest that there are at least three ways in which evolutionary psychological theory and research influences the larger field of psychology.

1. Evolutionary Psychology Opens New Linesof Inquiry in Psychology

The use of evolutionary psychological models sometimes generates novel hypotheses and lines of research that had not—andinmanycasescouldnot—bederivedfromothertheoretical models. One example of this point is the research on fluctuating asymmetry and reproductive behavior that was reviewed in this research paper. Another example is theory and research on father involvement and timing of daughters’ reproductive development. Draper and Harpending (1982, 1988) have proposed a middle-level evolutionary theory of the role of father involvement in the development of female reproductive strategies. This theory posits that individuals have evolved to be sensitive to specific features of their early childhood environments, and that exposure to different early environments biases individuals toward acquisition of different reproductive strategies. Specifically, Draper and Harpending proposed that an important function of early experience is to induce in girls an understanding of the quality of male-female relationships and male parental investment that they are likely to encounter later in life. According to the theory, this understanding has the effect of canalizing a developmental track that has predictable outcomes for girl’s reproductive behavior at maturity. Girls whose early family experiences are characterized by father absence (where women rear their children without consistent help from a man who is father to the children) perceive that male parental investment is not crucial to reproduction; these girls are hypothesized to develop in a manner that accelerates onset of sexual activity and reproduction, reduces reticence in forming sexual relationships, and orients the individual toward relatively unstable pair-bonds (Draper & Harpending, 1982, 1988). Belsky, Steinberg, and Draper (1991; see also Surbey, 1990) added to this theory the hypothesis that girls from paternally deprived homes should also experience earlier pubertal maturation. From an evolutionary perspective, early pubertal maturation, precocious sexuality, and unstable pair-bonds are integrated components of an accelerated reproductive strategy. During human evolution, this accelerated strategy may have promoted female reproductive success in ecological contexts in which male parental investment was not crucial to reproduction.

Although variation in the timing of pubertal maturation in girls is a socially relevant topic (i.e., early-maturing girls experience relatively high rates of breast cancer, teenage pregnancy, depression, and alcohol consumption; e.g., Vikho & Apter, 1986; Udry & Cliquet, 1982; Caspi & Moffitt, 1991; Graber, Lewinsohn, Seeley, & Brooks-Gunn, 1997), there was almost no research on the psychosocial antecedents of this variation prior to publication of the evolutionary model. This gulf occurred because no other theory of socialization and child development provided a framework for studying timing of puberty. Indeed, researchers operating outside of the evolutionary umbrella had never thought to look at the relation between fathers’role in the family and daughters’maturational tempo. With the introduction of the evolutionary model of pubertal timing (see especially Belsky et al., 1991), this topic developed into a fruitful new area of research. Most studies suggest that girls reared in father-absent homes reach menarche several months earlier than do their peers reared in father-present homes (Moffitt, Caspi, Belsky, & Silva, 1992; Surbey, 1990; Wierson, Long, & Forehand, 1993). Moreover, some of these studies have found that the longer the period of father absence, the earlier the onset of daughters’ menstruation (Moffitt et al., 1992; Surbey, 1990). However, not all studies (see Campbell & Udry, 1995) have found an accelerating effect for years of father absence on menarcheal age. Ellis and Garber (2000) found that years of stepfather presence, rather than years of biological father absence, best accounted for girls’ pubertal timing (suggesting a possible pheromonal effect). Finally, Ellis et al. (1999) present longitudinal data showing that father-effects on daughters’ pubertal timing involve more than just father-absent effects: Within father-present families, girls who had more distant relationships with their fathers during the first 5 years of life experienced earlier pubertal development in adolescence. Consistent with the original theorizing of Draper and Harpending (1982), the quality of fathers’ investment in the family emerged as the most important feature of the proximal family environment in relation to daughters’ reproductive development (Ellis et al., 1999).

2. Evolutionary Psychology Enriches Existing Bodiesof Knowledge in Psychology

The use of an evolutionary psychological perspective may enrich existing bodies of theory and data in psychology. Evolutionarypsychologicalmetatheory,togetherwithmiddlelevel evolutionary theories, provide a powerful set of methodological heuristics that can provide guidance on what paths to follow (e.g., suggesting new hypotheses and providing criteria for recognizing significant observations) and what paths to avoid (e.g., raising suspicion of certain explanations or observations).

Consider, for example, theory and research on sexual jealousy in humans. Psychologists working outside of an explicitly evolutionary framework have contributed to our understandingofjealousyinnumerousways.Alargebodyofempiricalresearch has documented an array of cultural, developmental, and personality correlates of jealousy; detailed models of the causes of jealousy have been constructed; and the clinical management of pathological jealousy has been investigated (see Salovey, 1991; White & Mullen, 1989). Psychologists working inside an evolutionary psychological framework have also addressed the topic of jealousy, and this research has enriched the extant literature on jealousy in at least three ways.

First, the use of an evolutionary psychological framework has led to a variety of novel hypotheses about sexual and romantic jealousy that have generated fruitful new lines of research on the topic (see Buss, 2000). For example, evolutionary psychologists have hypothesized that levels of jealousy experienced by men (but not women) and amounts of time and energy expended on mate retention by men (but not women) will be negatively correlated with partner’s age, regardless of one’s own age. This gender-specific, age-specific hypothesis is based on the supposition that men with young, reproductive-aged partners are most at risk of being cuckolded and thus investing in offspring who are not their own. Consistent with this hypothesis, Flinn (1988) found that the amount of mate guarding engaged in by men in a Caribbean village decreased significantly when partners were pregnant or postmenopausal. Furthermore, Buss and Shackelford (1997) found that the amount of mate retention behavior engaged in by men (but not by women) was inversely related to the female partner’s age, even after controlling for the male partner’s age.

Second, evolutionary psychological approaches have been instrumental in correcting certain errors regarding the nature of jealousy. For example, the contention that jealousy is entirely a socially constructed emotion—essentially determined by cultural factors such as social roles and political institutions (e.g., Hupka, 1991; Bhugra, 1993)—has been questioned by evolutionary psychologists. Evolutionary psychologists conceptualize sexual jealousy as a biological adaptation designed by sexual selection to reduce paternity uncertainty and the threat of relationship loss (e.g., Daly et al., 1982). Sexual jealousy should be a universal emotion that is experienced in all cultures when a valued sexual relationship is threatened by a rival. Although some writers have claimed that sexual jealousy does not exist in some cultural groups such as Samoans and the Inuit, not to mention the swinging couples of the 1970s, subsequent analyses have shown that jealousy truly is a cross-cultural universal (Buss, 2000; Daly et al., 1982) and a major motive for homicide throughout the world (Daly & Wilson, 1988).

Third, an evolutionary perspective may prove valuable in integrating various middle-level theories of sexual and romantic jealousy. An extensive psychological literature has documented that feelings of jealousy are related to such factors as relationship quality, rival characteristics, partner similarity, gender, and attachment style (see White & Mullen, 1989). Various social and cognitive models, such as appraisal theory (White & Mullen, 1989) and self-evaluation maintenance theory (DeSteno & Salovey, 1996), have been suggested to account for these relations.An evolutionary psychological approach to jealousy may help integrate such models by providing overarching explanations for why certain patterns of appraisal occur in the specific contexts they do, and why jealousy is modified by such factors as relative mate value and the characteristics of rivals (Buss, 2000).

3. Evolutionary Psychology Radically Changes Certain Domains of Psychological Inquiry

In some domains, evolutionary psychology has offered more substantive changes to the kinds of explanations employed by nonevolutionary psychologists. For example, the metatheoretical assumptions of sexual selection theory, as instantiated in parental investment theory and good genes sexual selection theory, have radically changed theory and research on mate selection and intrasexual competition. Before the systematic application of evolutionary theory to human mate selection, most work in the area emphasized proximity (the tendency to date and marry people with whom one has regular social contact) and matching (the tendency to date and marry people whose value on the mating market is similar to one’s own) as causal agents in mate selection (e.g., Myers, 1993). The proximity effect was explained as a function of the frequency of social interaction together with the principle that familiarity breeds fondness. The matching effect was conceptualized as an outcome of basic principles of social exchange.

Although proximity and matching are relevant to mate selection, the social models that were used to explain these phenomena have largely been supplanted by current evolutionary models of mating preferences and behavior. General principles of social exchange, familiarity, and interaction frequency simply proved inadequate to explain the facts about human mating. These principles could not account for universal differences between men and women in mate selection criteria (e.g., Buss, 1989), for systematic variation within each sex in orientation toward long-term versus short-term mating (e.g., Gangestad & Simpson, 2000), of for lawful variation across species in mating preferences and behavior (e.g., Trivers, 1985). It is just these types of questions that are addressed by parental investment theory and good genes sexual selection theory. Although some attempts have been made to integrate evolutionary and social exchange perspectives (e.g., Fletcher, in press; Kenrick, Groth, Trost, & Sadalla, 1993), the bottom line is that evolutionary psychological models have dramatically changed the nature of research on mating preferences and behavior (as reviewed in this research paper).

Future Directions

In this research paper we have introduced some of the core ideas and assumptions that comprise the field of evolutionary psychology. We have also illustrated how these ideas can be employed in the development of specific, testable hypotheses about human mind and behavior. The rapid growth in publications in the area of evolutionary psychology over the past decade suggests a growing acceptance of the importance of evolutionary ideas in the behavioral sciences. What can we expect, however, from evolutionary psychology in the twenty-first century? What are the crucial issues that need to be addressed by evolutionary psychologists, and how are evolutionary psychological ideas likely to influence the various subdisciplines of psychology?

Perhaps the most crucial task for evolutionary psychologists in the coming decades will be the identification and elucidation of psychological adaptations. As Buss (1999) notes, evolutionary psychologists have catalogued most of the obvious and plausible psychological adaptations (especially those relating to human mating), but many more remain undiscovered or inadequately characterized. The concept of biological adaptation, as George Williams (1966) has noted, is an onerous one and should only be deployed if the appropriate sorts of evidence to make such a claim are available. Because adaptations are the product of natural selection operating in ancestral environments, and because psychological traits such as jealousy, language, and self-esteem are not easily reconstructed from fossils and artifacts, direct evidence for biological adaptations may be difficult to come by (Lewontin, 1998; Richardson, 1996). One of the challenges for evolutionary psychology, therefore, will be to develop increasingly more rigorous and systematic methods for inferring the evolutionary history of psychological characteristics (see Durrant & Haig, 2001).

How best to characterize psychological adaptations also remains an important issue for evolutionary psychology. As we have seen, evolutionary psychologists assume that the human mind comprises a large number of domain-specific psychological mechanisms that have evolved to solve specific adaptive problems in our evolutionary past. However, many important questions remain regarding the relative specificity of such mechanisms, the way that they might develop over time in response to different environmental contexts, and how these mechanisms operate in terms of proximate cognitive and neurobiological processes.

Consider, for example, the theory that self-esteem acts as an interpersonal monitor—or sociometer—that tracks the membership status of individuals in social groups (Leary & Downs, 1995; Leary, Tambor, Terdal, & Downs, 1995). Leary and colleagues approached this well-studied psychological phenomenon by asking the important question: What is the (evolutionary) function of self-esteem? Their answer is that people do not strive for self-esteem as some kind of end point or ultimate goal. Rather, self-esteem reflects one’s level of relative social inclusion or acceptance in social groups. Selfesteem, therefore, functions to motivate individuals to pursue courses of action that can restore or improve their acceptance by relevant others. In short, the self-esteem system is characterized as a psychological adaptation that has evolved to solve the recurrent adaptive problem of social exclusion and the fitness costs that such rejection would have entailed in ancestral environments.

However, many important questions remain regarding the nature of the self-esteem system, even if it can be plausibly considered a psychological adaptation. For example, Kirkpatrick and Ellis (2001) have suggested that one should expect self-esteem to be carved in to multiple domains to reflect the different types of interpersonal relationships that were important during human evolutionary history. Thus, they argue that there will be a number of different sociometers that gauge relative social inclusion in such domains as mating relationships, family relationships, and instrumental coalitions. Just how many different sociometers humans possess, however, remains an open question. Furthermore, we are only beginning to understand how the mechanisms underlying self-esteem develop over time in response to different environmental contexts and how they operate at a proximate cognitive and physiological level. One of the important challenges for evolutionary psychology, therefore, lies in fleshing out the details of putative psychological adaptations such as self-esteem.

Over the next couple of decades, we expect that the coherent body of theory developed by evolutionary psychologists will be applied more regularly to many new fields in the behavioral sciences, especially such applied domains as organizational, environmental, and clinical psychology. For example, within clinical psychology, evolutionary explanations have been recently advanced for a variety of specific disorders, such as depression (Price et al., 1994), phobias (Marks & Nesse, 1994), substance abuse (Nesse & Berridge, 1997), and autism (Baron-Cohen, 1995). Even the very basis of the classification of mental disorders has been reconceptualized from an evolutionary perspective (Murphy & Stich, 2000). Specifically, Murphy and Stich urge that we should draw a fundamental distinction between mental disorders that arise from the malfunction of specific evolved psychological mechanisms, on the one hand, and those that occur due to a mismatch between our evolved psychological architecture and contemporary environments, on the other. Thus, autism can be plausibly conceptualized as the result of a malfunctioning of the theory of mind module, which has evolved to make inferences about others’ behavior on the basis of imputed mental states such as beliefs and desires (Baron-Cohen, 1995). Depression, by contrast, as conceptualized by the social-competition model (Price et al., 1994), may result from increased likelihood of drawing unfavorable comparisons with other individuals due to the enlarged size of our potential social groups, brought about by population growth and advances in information technology.

In suggesting that evolutionary psychology will expand into new domains, we do not mean to imply that extant psychological theories will be overthrown or replaced. Rather, as more is known about the evolutionary origins of the human mind, more integrated theories can be developed—ones that recognize the important role of multiple explanations drawn across different levels of analysis.

In conclusion, Homo sapiens, like all other species, is the product of a history of evolution. Our opposable thumb, bipedal stance, and color visual system are all testimony to the gradual process of natural selection operating over vast spans of time. Just as the anatomical and physiological features of our bodies are explicable in evolutionary terms, so too are the complex array of psychological processes that make up the human brain-mind. The rapidly growing field of evolutionary psychology—from its broad metatheoretical assumptions to the specific predictions that are tested in research—offers a coherent and progressive paradigm aimed at uncovering the origins and functions of human mental and behavioral characteristics. In this research paper we have offered an introduction to some of the key ideas, issues, and methods that guide applications of evolutionary theory to human cognition and behavior. Although evolutionary psychology still meets resistance on some fronts, we believe that its value and potential for investigating questions of human nature is great.

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essay topics for evolutionary psychology

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Evolutionary Psychology

Sociobiology

Reviewed by Psychology Today Staff

The human body evolved over eons, slowly calibrating to the African savanna on which 98 percent of humankind lived and died. So, too, did the human brain. Evolutionary psychology is the study of the ways in which the mind was shaped by pressures to survive and reproduce. Findings in this field often shed light on "ultimate" as opposed to "proximal" causes of behavior. Romantic jealousy and mate guarding are proximally intended to keep one's relationship intact. Ultimately, though, the behavior can be explained by the fact that for most of human history, losing a romantic partner jeopardized one's ability to reproduce and raise children.

  • The Science of Evolutionary Psychology
  • Concepts In Evolutionary Psychology
  • Human Nature, Explained
  • Why Evolutionary Psychology Is Controversial

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Natural selection has a lot to do with human behavior. In fact, our behavior is naturally selected just as our physical traits are naturally selected. We are much taller and live longer than our ancestors. Through centuries of generations, evolution has helped us pass along adaptive behaviors that promote our reproduction.

Evolutionary biologist Robert Trivers proposed a number of theories on evolutionary psychology , including why we engage in reciprocal altruism , the nature of sex differences, and parent-offspring investment. Altruism among strangers, for example, can naturally develop because people cooperate with the expectation of receiving similar treatment from others.

Our hunter-gatherer ancestors passed down behavioral traits that are, for the most part, advantageous to us. For example, we are mindful of danger in dark alleyways. This caution is innate and within our behavioral make-up. And our predetermined response to gravitate to that 800-calorie Cinnabon can wreak havoc, but our ancestors made us do it .

Juggling our ancestral tendencies with the demands of modern-day living can be a struggle. This phenomenon is known as evolutionary mismatch—when we find ourselves in an environment inconsistent with our ancestral conditioning.

A good example of such mismatch is the contemporary diet : Ten thousand years ago, people battled starvation. They had to pile on the necessary calories just to survive certain lean times; high-fat meats and high-sugar foods were a luxury. Today, however, fatty foods and processed sugars are readily available at low cost.

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Many of the behaviors people exhibit have been tools for self-preservation: Homo sapiens jealously guard their romantic partners because competition for mates has always been harsh. Everyone cherishes their closest kin because it's in one's best interest to preserve one's genes . Humans also crave social interaction to encourage cooperation , further increasing the chances for survival. Many of these behaviors are innate: How people react and interact with one another is spelled out in DNA.

Fight or flight refers to the human body’s built-in response to a perceived threat: It prepares the body to either face danger or quickly run from it. During flight or flight , the brain releases stress hormones , pushing the body into high alert. The heart rate rises, muscles tense, and thoughts race. While the modern-day human does not face the same threats as our ancestors did, the fight-or-flight response system remains intact.

Any fearful situation can trigger it, whether it is physical danger or a stressful event, like running late for a meeting. In people with anxiety , the fight-or-flight response is more readily triggered, the brain sees certain situations as threatening, even when there's no actual present danger. In fact, there is a tendency for this response to move into overdrive in anxious individuals.

Kin selection is the theory that our calculations about genetic relatedness to others (conscious or unconscious ) are powerful drivers of behavior. Most people favor, and will make sacrifices for, immediate kin as opposed to distant relatives, and blood relatives over strangers. This ensures the survival of genes through the survival of the people who are closely related to us.  

In evolutionary parlance, reproductive success is called reproductive fitness, a measure of how well an organism or a person is adapted to their environment. Men committing foolish or heroic acts that increase status or attractiveness are acting in ways that increase the odds of reproduction, and attempting to maximize reproductive fitness.  Reproductive fitness  also measures how well an organism is adapted to its environment.

The differences in parental investment —the energy and resources invested in an offspring—lead the sex that invests more (females, in most species) to focus on mate quality and the sex that invests less (males) to seek quantity. In humans, we expect choosiness in females and aggression between males as they vie for females.

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Our emotional complexity differentiates us from other members of the animal kingdom. Evolutionary psychology seeks to explain how our emotions and other aspects of being human served as advantages to our ancestors. Like other social primates, we experience emotions beyond primal fear and anger.

Through evolving as a group, we have developed empathy and altruism, which allow us to commiserate with each other’s circumstances and act in ways that are not self-serving. What is better for the group as a whole, is better for a person as an individual.

We have also developed emotions to help keep us in line —for example, shame motivates us to atone for past transgressions, while pride pushes us to remain in the high regard of our peers. And as our social structures developed, so did our value systems and what we define as “right” and “wrong.”

Trivers also suggested that complex strategies of cheating , detecting cheating, and the false accusation of cheating (itself a form of cheating) pushed the development of intelligence and helped increase the size of the human brain.

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People reject evolutionary psychology for ideological reasons. With sexual behavior, for example, there is the notion that the field justifies people’s behaviors and actions. Our present-day traits and characteristics had survival value for our ancestors, and these traits survived because the genes they are linked to were selected and now remain part of our genetic makeup. Shouting evolution made me do it seems so convenient.

This refers to common but faulty logic wherein people assume that because something is "natural" it is therefore "good" or just. Violence and aggression are found in all human societies, but that does not make this acceptable behavior. No endorsement is implied in a discovery of what is natural. The general public commits the naturalistic fallacy in thinking that evolutionary psychologists endorse certain findings (such as violence or rape), when in fact evolutionary psychologists are simply outlining reasons that these behaviors may occur.

The moralistic fallacy is the false belief that the world operates as we wish it would, that what ought to be is in fact the truth, or that because we wish something were not true, it cannot be true. People sometimes reject evolutionary theorists' findings about human nature because they do not want to believe that said findings are true.

Both sides of the political aisle accuse evolutionary psychology of numerous ills. Among many arguments, for example, conservatives on the right fear that this field of study absolves people of responsibility , while liberals on the left fear that accepting inherited differences hinders the goal of social equality.

Feminists are not keen on the idea that women are inherently different from men. Such differences, they think, would force women back in time, losing ground in equal opportunity and equal pay, for example. They also feel that people can use evolutionary psychology to explain away misogyny, poverty, sexual misbehavior, among many areas.

More and more studies show that homosexuality is genetic. However, being gay doesn’t fit so neatly into the theory of natural selection. Why would nature select for homosexuality if reproductive success is a moot point? But there are valid reasons according to evolutionary biologists. For example, gay aunts and uncles can invest more time and resources in rearing the offspring of close relatives with whom they share part of their genetic makeup. Maybe homosexuality emerged because it benefits entire groups.

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Theoretical Insights of Evolutionary Psychology: New Opportunities for Studies in Evolutionary Ethnobiology

  • Published: 29 January 2020
  • Volume 47 , pages 6–17, ( 2020 )

Cite this article

  • Joelson Moreno Brito Moura 1 , 4 ,
  • Risoneide Henriques da Silva 1 , 4 ,
  • Washington Soares Ferreira Júnior 2 ,
  • Taline Cristina da Silva 3 &
  • Ulysses Paulino Albuquerque   ORCID: orcid.org/0000-0002-8131-8429 4  

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In this article, we present the central ideas of evolutionary psychology, and discuss how their assumptions can help ethnobiologists to understand the dynamic relationship between people and their environments. In this sense, investigating this relationship from an evolutionary perspective can bring new empirical evidence about human evolution, also contributing to both evolutionary psychology and evolutionary ethnobiology.

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essay topics for evolutionary psychology

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Acknowledgements

This study was financed in part by the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - Brasil (CAPES) - Finance Code 001. Contribution of the INCT Ethnobiology, Bioprospecting and Nature Conservation, certified by CNPq, with financial support from FACEPE (Foundation for Support to Science and Technology of the State of Pernambuco - Grant Number: APQ-0562-2.01/17). Thanks to CNPq for the productivity grant awarded to UPA. We also acknowledge the CAPES for the grant awarded to JM, and the Fundação de Amparo à Ciência e Tecnologia de Pernambuco (FACEPE) for the grant awarded to RHS. To the anonymous reviewers who improved our paper with their comments.

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Moura, J.M.B., da Silva, R.H., Ferreira Júnior, W.S. et al. Theoretical Insights of Evolutionary Psychology: New Opportunities for Studies in Evolutionary Ethnobiology. Evol Biol 47 , 6–17 (2020). https://doi.org/10.1007/s11692-020-09491-0

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The Evolutionary Psychology of Envy and Jealousy

Vilayanur s. ramachandran.

1 Center for Brain and Cognition, University of California, San Diego, San Diego, CA, United States

Baland Jalal

2 Behavioural and Clinical Neuroscience Institute, Department of Psychiatry, University of Cambridge, Cambridge, United Kingdom

The old dogma has always been that the most complex aspects of human emotions are driven by culture; Germans and English are thought to be straight-laced whereas Italians and Indians are effusive. Yet in the last two decades there has been a growing realization that even though culture plays a major role in the final expression of human nature, there must be a basic scaffolding specified by genes. While this is recognized to be true for simple emotions like anger, fear, and joy, the relevance of evolutionary arguments for more complex nuances of emotion have been inadequately explored. In this paper, we consider envy or jealousy as an example; the feeling evoked when someone is better off than you. Our approach is broadly consistent with traditional evolutionary psychology (EP) approaches, but takes it further by exploring the complexity and functional logic of the emotion – and the precise social triggers that elicit them – by using deliberately farfetched, and contrived “thought experiments” that the subject is asked to participate in. When common sense (e.g., we should be jealous of Bill Gates – not of our slightly richer neighbor) appears to contradict observed behavior (i.e., we are more envious of our neighbor) the paradox can often be resolved by evolutionary considerations which h predict the latter. Many – but not all – EP approaches fail because evolution and common sense do not make contradictory predictions. Finally, we briefly raise the possibility that gaining deeper insight into the evolutionary origins of certain undesirable emotions or behaviors can help shake them off, and may therefore have therapeutic utility. Such an approach would complement current therapies (such as cognitive behavior therapies, psychoanalysis, psychopharmacologies, and hypnotherapy), rather than negate them.

Human emotions are very poorly understood even though there is a long venerable tradition of research pertaining to them, going all the way back to Darwin’s “Expression of Emotions in Animals and Men” ( Darwin, 1872 ; on emotions see also Ekman and Friesen, 1971 ; Izard, 1977 ; Wierzbicka, 1986 ; Russell, 1994 ; Oatley and Jenkins, 1996 ; Fredrickson, 1998 ; Lewis, 2000 ; Panksepp and Biven, 2012 ). This is in stark contrast to research on such arcane topics as – say, apparent motion perception which has been studied in excruciating – sometimes pointless – detail. In truth our “common sense” understanding of emotions is probably closer to the mark than the insights offered by specialists working on the subject (just read a good Jane Austen novel).

One problem is that physiologists and psychologists who study emotions do not look at them enough from an evolutionary standpoint (for exceptions, see Nesse, 1990 ; Ekman and Davidson, 1994 ; Johnston, 1999 ; Cosmides and Tooby, 2000 ; Tooby and Cosmides, 2008 ). This is unfortunate because as Dobzhansky famously said, “Nothing in biology makes any sense except in the light of evolution.” This may seem obvious but even though people often pay lip-service to it, it is an attitude that has yet to permeate mainstream neurology and psychology [as championed eloquently by Tooby and Cosmides (1990) ].

In evolutionary terms, emotions are adaptive responses to the environment that increase my chances of survival. But unlike simple adaptations – say the sensation of pain when my hand is pocked with a hot rod motivating me to withdraw it – emotions are much more complex. They orchestrate a more organized response. If I suspect a tiger is nearby, a fight/flight reaction (mediated by limbic structures) will activate several aspects of my physiology and cognition, each recursively feeding on the other – influencing my behavior (e.g., Nesse and Ellsworth, 2009 ).

It is of course possible to swing to the other extreme and assume that every little quirk of human behavior must have a module devoted to it that has direct survival value that was honed by natural selection; a view perpetuated by media accounts of evolutionary psychology (EP) (although the main proponents of this approach are usually careful to avoid such pitfalls, including David Buss, Donald Symons, John Tooby, Leda Cosmides, Melvin Connor, Christine Harris, and Steven Pinker). There are four pitfalls to watch out for in taking this approach: (1) Not everything is adaptive; many quirks of mind may be incidental byproducts or atavistic remnants of things that were once useful (the psychological equivalent of the vermiform appendix). (2) The second pitfall is that many so-called universal psychological traits may be learned; people may have “converged” on the same solution to similar environmental challenges; e.g., cooking is almost universal but we do not postulate a cooking-module in the brain hardwired through natural selection. It was probably based on the accidental discovery of game roasted by forest fires. (3) Both the observed trait and its explanation are banal; obvious even to your grandmother. For example, men like young women with clear skin and big breasts because they are more fertile; so the genes that predispose to such preference would multiply. Is there anyone who doesn’t know this? (4) When the explanation is not banal then it is often very difficult – almost impossible – to test experimentally or refute. It fails to fulfill the falsifiability criterion of Popper. A good example is the satirical theory one of us proposed to account for why “gentlemen prefer blondes” ( Ramachandran, 1998 ), suggesting that they do so because it allows them to detect early signs of parasitic infestation and aging – both which reduce fertility. In addition, reciprocity of sexual interest is more obvious in blondes because of the dilatation of dark pupils against a pale iris; as is the pink flush of orgasm in a light skin – which lowers the chances of cuckoldry and increases likelihood of implantation. (Blushing, too, is more obvious in blondes who in effect is sending an involuntary “truth in advertising” signal conveying that she can’t cucold with impunity without the blush of embarrassment giving her away.) This account was taken seriously by some members of the EP community; indeed, we concede the possibility that what began as a satire may have more than a grain of truth in it! An even more far-fetched theory was proposed jocularly by my colleague JA Deutsch (personal communication). Deutsch suggests that the reason women experience nausea and vomiting early in pregnancy is because “the odor of vomitus” would discourage the husband from having sexual intercourse with her. This makes evolutionary sense given the known risk of abortion resulting from intercourse in such cases. As a final example, let us suggest that the reason we flock to aquaria is that our Devonian piscine ancestors were attracted to other fish and we have remnants of this affinity fossilized in our brains. It is easy to see the absurdity of these three examples, but some EP arguments have the same form.

Where EP is on firm ground is when it avoids as many of these pitfalls as possible. Then it becomes fun to explore. The name of the game is to make observations of human psychology that initially seem surprising, counterintuitive, and apparently non-adaptive and then go on to show there might be a hidden evolutionary agenda. This strategy does not necessarily prove the theory but it makes it more credible than if the pitfalls had not been avoided. We would like to illustrate this approach by considering the very simple example of jealousy or envy. These two words are used interchangeably in the United States, but in the United Kingdom the former is more often used in a sexual context, the latter in other contexts. In either case the “target” is usually someone who is perceived to be better off in some respect than you or whose access to resources is better than yours. Jealousy also has a possessive component; I want to actually deprive the other person’s resource and claim it as my own. It is a negative emotion. Envy is not quite as negative – it does not have the same sharp edge and it motivates emulation to gain independent access to similar or even better resources. The extreme along the same spectrum would be pure admiration of someone, who, through inborn talent and intense effort, is better off than you. I am envious of my neighbor who got an award from the local mayor, but I admire Francis Crick.

Jealousy is a motive of immense potency. Although you are often consciously aware of being jealous or envious of someone, sometimes the actual reasons for the envy are buried in your unconscious and disguised by rationalizations. Ironically, what you really value in life is more often revealed by asking yourself who you are jealous of rather than asking yourself directly “what do I value.” The latter often taps into what society expects you to value; your “superego” takes over – and you are aware only of what you should want rather than what you really want. Envy and jealousy, on the other hand, kick in as a gut reaction in your emotional/evaluative system long before you become conscious of it.

Introspection is unfashionable in contemporary psychology largely due to the lingering effects of behaviorism. Contrary to this view, we will argue (and demonstrate in this paper) that introspection (if accompanied by cross-validation across other thoughtful subjects) can be a valuable source of insights into the internal logic and evolutionary rationale of certain complex emotions like envy. Obviously, objections can be rightfully raised against the – purely subjective – exercise of introspection, which is why it is imperative to eventually test these conjectures by making counterintuitive predictions that can be empirically falsified (using a rigorous scientific approach). But meanwhile one can have fun speculating on possibilities.

The central argument in this paper is that one can achieve a deeper understanding of emotions by introspective “thought experiments”; asking yourself – and others – which social situation (A or B) would make you more prone to that emotion and what the environmental triggers are. One can then construct meaningful evolutionary scenarios as to why a particular trigger (A) might have evolved to produce a given emotion even though common sense might dictate that another trigger (B) should be more effective. For the more flagrant emotions (like aggression) the triggers and their evolutionary rationale are obvious and probably mediated by limbic structures in the brain. But more complex emotions require more complex triggers (or combinations of them) to elicit them. The evolutionary logic of these emotional triggers may not be obvious at first but can be teased apart – by imagining yourself in certain situations and simply asking yourself how you would feel. Most complex emotions may depend strongly on social interactions, context, self-worth evaluation, and a sense of who you are as perceived by others. Examples would include pride, arrogance, superciliousness, ambition, guilt, gratitude, and jealousy (the topic of this article). Unlike basic emotions like aggression and fear – mediated mainly by the limbic fight/flight response, these more complex emotions probably require interactions with the orbitofrontal cortex. Such emotions, including the ability to introspect on them (“I am jealous because, etc.”) are probably unique to humans or especially well developed in us. They may require the construction of a “meta-representation” – a representation of earlier representations in the brain (knowing that you know, or knowing that you are jealous).

It raises an important issue. Do the subtler emotions (like pride, ambition, envy, and guilt) each have a peculiar flavor. For example, does jealousy have its own unique subjective qualia or is it a vague nebulously negative feeling that becomes either tinged with its unique “flavor of jealousy,” or is it merely inferred post hoc , based on social context? Unlike (say) the quale of red which kicks in right away independent of social context? Introspection suggest the former; for we often catch ourselves experiencing a twinge of jealousy of a friend – often with surprise and embarrassment – before inferring the reasons, context, etc.

We would venture that a frontal patient may still be capable of aggression, fear, and lust but not of envy or romantic love (which have complex and subtle social dimensions). Such a patient will have great difficulty introspecting on his own emotions – not just expressing them. In evolutionary terms, it is worth noting that even though emotions are privately experienced almost all of them are meaningless except in relation to others; i.e., in a social context (e.g., envy, pride, jealousy, and kindness). This is partially true even of the more basic emotions such as fear, lust, anger, and pain; for instance, we shout “ouch” to attract attention.

What triggers jealousy, beyond the obvious of someone who is better off? And can the functional logic of these triggers (or peculiar combination of social cues) be explained in evolutionary terms; i.e., what might be their survival value? Through introspecting on ourselves and through informally surveying friends, students, colleagues, etc., we composed the following list. For each item on the list, we will try to come up with a plausible evolutionary scenario. Especially important is the question of why you make a particular choice even though common sense might favor the other choice. We would emphasize that these are at this stage merely preliminary informal surveys, whose goal is to prompt further inquiry using rigorous methodology to collect formal data. (In the study of visual perception, analogously visual illusions have a long and venerable tradition in making important points long before detailed measurements were made to confirm those points).

(1) Are you more envious of: (A) someone who is similar to you in most respects but is a bit wealthier (say 50% wealthier) or (B) more envious of Bill Gates? Is a beggar jealous of a slightly more successful beggar or of Bill Gates?

The answer is almost always the former (10 out of 11 people we surveyed chose A). This does not make sense. One usually expects the strength of an emotion to be directly proportional to the resource being sought after; e.g., blood glucose determines the degree of hunger. Following this argument, shouldn’t you be more envious of Bill Gates? Common sense might dictate that the better off someone is than you are, the more envious you should be. But counterintuitively this isn’t true. “Common sense” (the logical or reasoning part of the brain) of course also arose through evolution – but arguably for different needs; i.e., abstract generalizations such as rules of logical inference – which have only limited access to the “laws of emotions” (keeping in mind the modular architecture of the human brain). You ought – logically – to be more jealous of Bill Gates because he has more resources. But the “emotion module” is wired-up for immediate “gut-reactions” like jealousy, sometimes overriding logical inferences. In general, gut-reactions and the “rationality faculty” deliver consistent answers – but not always.

Where conventional EP theories sometimes fall short is that they aren’t always counterintuitive. For example, they “explain” that men prefer younger women because they are more fertile. Neither the phenomenon itself (the choice of younger women) nor the standard explanation (“they are fertile”) is counterintuitive. They fail to fulfill what we call the “grandmother test” – what your grandmother might have deduced from the mere application of common sense. The trouble is that in many scenarios commonly considered in EP, these two (common sense vs. hidden evolutionary agenda) make the same prediction; the only way to dissociate them is to create highly contrived scenarios; which we shall attempt, in this paper.

What is the evolutionary logic that drives envy; e.g., the fact that you envy your neighbor more than Bill Gates? The answer is that the whole purpose of envy is to motivate you into action either by independently trying harder (envy) or by coveting and stealing what the other has (jealousy). This is why jealousy has an aggressive component, but envy is more positive sometimes even being tinged with admiration.

Turning to Bill Gates vs. a more prosperous beggar, we believe this can be explained quite readily by the axiom that envy evolved to motivate access to resources that are in demand by others in your group. If I am the poor beggar my brain quickly computes that in all likelihood the very rich Gates is either deservedly much richer (i.e., he is far smarter), or just extremely lucky. Evolutionarily speaking, there is no point in being jealous of him because he is “off scale” either in ability or luck, so no amount of effort by me can result in reaching his level of prosperity; envy would motivate an inappropriate and futile waste of resources. The richer beggar, on the other hand, may be only slightly smarter, luckier, or more hardworking than me, so there is some chance, at least, that envy might motivate me to exceed his access to resources (or jealousy might make me steal it away from him with impunity).

(2) Are you more envious of (A) someone equal to you in talent, effort, etc., but he/she gets undeservedly promoted over you or (B) of someone who is genuinely better than you, who is rewarded?

The answer is almost always “A” (11 out of 11 people we surveyed chose A). Again, note that this makes no obvious sense; if you want to be as rich as your neighbor, what does it matter whether he was undeservedly rewarded or legitimately rewarded. This can be teased apart further. For example, does it matter whether the other guy got rewarded by the boss, (A) because he is (naturally) genetically more intellectually gifted than you, (B) more hard working, or (C) arbitrarily for no reason? EP would predict that you would be most envious of “B” because the envy would motivate you to do something about it, whereas competing with “A” might be futile; you cannot over-ride genetic endowments. (You might be angry at the boss for being unfair, but not jealous of the recipient.) “C” would make you envious too if “doing something about it” includes complaining to your boss. The greater envy for “B” over “A” should be especially true if “A” is vastly better endowed than you genetically; if he is only slightly better endowed then some envy would be useful – motivated hard work can help you to overcome genetic limitations. This would be analogous to the beggar vs. the other beggar scenario provided above. The third scenario (C) would not provoke envy; it would provoke anger toward the person who unfairly rewards your neighbor. In short, we can show that even though a surface-level analysis of a human psychological propensity makes it seem maladaptive, there is often an evolutionary hidden agenda that drives that propensity, and makes it comprehensible. We are not making a definitive argument here but hopefully providing food for thought.

(3) Let us say I were to prove by brain scans or some other reliable measure (e.g., mood/affect inventory) that (A) the Dalai Lama was vastly happier on some abstract, but very real, scale than (B) someone (say Hugh Heffner) who has limitless access to attractive women. Who are you more envious of?

Most men are more envious of the latter (9 out of 9 males we surveyed chose B). In other words, you are more jealous of what the other person has access to (in relation to what you desire), than of the final overall state of joy and happiness. This is true even though common sense might dictate the opposite. Put differently, evolution has programmed into you an emotion (jealousy) that is triggered by certain very specific “releasers” or social cues; it is largely insensitive to what the other person’s final state of happiness is. The final state of happiness is too abstract to have evolved as a trigger of envy or jealousy.

For similar reasons, if you are starving it makes more sense that you would be more jealous (at least temporarily) of someone enjoying a fine meal than someone having sex with a beautiful woman or man. If you are only slightly hungry, however, you might pick sex. This is because there is an unconscious metric in your brain that computes the probability of finding food in the near future vs. finding a nubile, available mate; and of the urgency of your need for food over the urgency of mating. If you are starving to death and have one last fling, you have only that single mating opportunity whereas if you eat and live you will have plenty of mating opportunities in the future.

(4) Imagine a scenario (A) in which you see another guy/girl making love to a woman/man you are attracted to and desire. You are jealous. But what if (scenario B) you see the same guy/girl having even more passionate sex with a woman/man you are not attracted to.

Surprisingly, you are more jealous of him/her in “A” (13 out of 15), even though one might expect the answer to be “B” – i.e., you should be jealous of and strive to achieve – his final pleasurable state (B) than what leads up to it (A). Again evolution prevails over common sense in a very specific manner. You have a metric in your head (your assessment of your own attractiveness constructed unconsciously by monitoring the frequency and “objective beauty” of other women who were attracted to you in the past) of what you want and are capable of. These triggers determine who or what you are jealous of, even though it doesn’t make any sense. The situation is not fundamentally different from you eating cotton candy. Even though you know rationally it is not good for you, these “carbohydrate binges” were wired into your brain during prehistoric times when food was scarce to help tide over dry spells of famine. In the case of food preference, this idea might seem obvious (although it wasn’t obvious to us until Steven Pinker spelled it out). But in the case of more complex emotions like jealousy, the idea has not been adequately explored in the manner attempted in this article. The general idea is that even complex and subtle nuances of a certain emotion can be analyzed in this manner.

(5) Another example also illustrates how some emotions despite being counterintuitive and seemingly illogical initially reveal a hidden evolutionary agenda. (A) You see your neighbor (who is similar to you in most respects) having moderately enjoyable sex with a woman whom you moderately covet; (B) you see two ugly tramps having intensely pleasurable sex with each other. Who would elicit more envy?

Again, for reasons already alluded to, most people are more envious of “A” (12 out of 15 people we surveyed chose A). This is another example of being envious, not of the final level of intense pleasure (as one might naively expect) but of someone having access to – and only slightly enjoying – something for which you have a modest desire and will only modestly enjoy (but access is denied). Thus, we see that what triggers envy are certain social cues; “happiness” is too abstract to be envious of. All this seems plausible but – once again – we emphasize the need for caution in interpreting such data. You might avoid choosing the tramps not because of the evolutionary reasons alluded to above but because any association with tramps elicits avoidance.

In general, the less complicated or contrived the thought experiment, the more straightforward the result and the interpretation. The simplest example of the genre of thought experiments discussed so far would be; would you be more jealous of (A) your neighbor who is slightly smarter than you who gets a huge raise and award for her performance – or (B) you and she each buy a lottery ticket and she ends up winning 500,000 dollars? If you introspect, your answer like that of most people might be that you would be less jealous in the second scenario (lottery) because you recognize that no amount of extra motivation from you (driven by jealousy) could repeat a fluke accident.

We now introduce the concept of “relevant social circle”:

(6) Imagine you are a first generation Indian immigrant in the United States; (A) your neighbor is also an Indian immigrant of comparable talent; (B) a Chinese immigrant; (C) an American local. Say “A” has something you covet and you envy him; “B” has the same thing and “C” does too. Who would you be most envious (jealous) of? Let us say for the sake of argument that what all of you covet is a woman or man.

Most would envy “A” more than “B” or “C” (11 out of 11 we surveyed chose A). It is the unconscious metric again. Your brain says (in effect), “A” has had the same privileges, opportunities, status, etc. as me, so there is some point in my being envious of him in order to motivate me, since I have at least some chance of gaining access to the same resources; he provides an “existence proof” that someone who is very similar to me can have access to the same resource. “B”, on the other hand, is a complete unknown. Finally, “C” may be favored for completely arbitrary reasons such as racism and xenophobia against a member of the more privileged majority White American culture. Unlike “A”, “C” has most likely had more privileges and opportunities throughout his life, so there is not much motivation for you to compete, as you don’t have a chance of gaining access to his resources – thus envy would lead to a futile waste of resources and time. Instead, the evolutionary consequence might be anger toward “C”, rather than an attempt to compete and balance the inequity through personal effort (you wouldn’t be jealous). Obviously, in many situations the two emotions overlap.

(7) Geographic proximity; this is, a special case of the “relevant social circle” effect: Compare the two cases: (A) Joe lives in Timbuktu. He is very similar to you in talent, looks, capacity for work, etc. but he is twice as wealthy as you; (B) Joe is your neighbor and twice as wealthy.

Most people would be envious of “B” more so than “A” (11 out of 11 we surveyed chose B). Again this makes evolutionary sense. There are millions of people who are like “A” and even though I have assured you logically that they are identical to “B”, your brain requires more direct triggers. On the other hand, you see and interact with “B”, and this is a direct trigger for envy to kick in. “A” is simply too abstract to relate to and, more importantly, is not competing for the same resources as you (and is, in any event, too far from you to do anything about). There would be no motivation to work harder since even if you did, you would not gain access to resources in Timbuktu. You might admire him – even emulate him – from a distance, but it would be futile to be envious.

(8) There is a very attractive woman (or man) you have your eye on and have reason to believe that you are within her range of acceptability and is attracted to you. But another man walks in and she is instantly attracted to him and walks off with him. He is one of three people: (A) he is stunningly handsome and wealthy and walks off with her; (B) only slightly better looking and handsome or even identical to you in most respects; and (C) an ugly old poor tramp. Who would you be most jealous of?

Most people are jealous of “B” (8 out of 11 people we surveyed chose B). After “B” we suggest that people would be jealous of “A” and then “C.” The reason we suggest this is that as a motivator of action, jealousy would be most likely to be effective in situation “B.” Jealousy might be futile in “A,” and you can’t blame him (or her) in succeeding in tempting her away. Lastly, the behavior of your potential target mate in “C” – her choice of an ugly tramp – suggests that her choices are completely idiosyncratic and unpredictable. So there is not much point in even trying.

Jealousy for siblings is a special case. Since a sibling [whether identified correctly or misjudged to be a sibling as a result of close proximity from early childhood (i.e., “the kibbutz effect”)] shares half your genes you should theoretically be less jealous of his access to resources than you would be of a complete stranger. But this is complicated by the fact that you are in direct competition for the same food resources (e.g., during weaning) delivered by parents and by the “relevant social circle” phenomenon predicted above. The net result would be a complex hybrid of emotions, as is often indeed the case with siblings. For the same reason, we would predict that jealousy of parents should be a rarity.

We reiterate that the data presented here are merely preliminary surveys rather than derived from formal research. While introspection can be a valuable source of insight as a starting point, these conjectures must eventually be tested using empirically sound methods. What we have introduced is just the bare skeleton outline of the evolutionary logic that might be driving jealousy. There are bound to be other complex contextual and personality variables that influence any particular individual’s choice in each of these far-fetched scenarios. Nevertheless, these speculations might provide a starting point for a more sophisticated understanding of jealousy than has been hitherto possible, taking us well beyond our “common sense” understanding of this complex human emotion. We believe a similar strategy could be applied for understanding other equally complex human emotions. The goal is to seek the “ulterior motive” in strictly evolutionary terms, of forms of behavior that might initially seem inexplicable. Conversely, pointing out that men like big breasts of young women simply doesn’t cut it; EP does not tell you anything that common sense doesn’t [see Konner (2015) for an elegant exception].

We have considered only one example, namely, jealousy – to illustrate our strategy but, obviously, one could apply it to other emotions. Consider embarrassment, for example. If you are a man buying an adult erotic DVD, would you be more embarrassed if the sales clerk at the cash register was: (A) a handsome young man; (B) a beautiful woman; (C) an old lady; and (D) an ugly old man? The answer is usually “B” or “C” (11 out of 13 males chose either “B” or “C”) but why? And might not the answer give us novel insights into the evolutionary origins of embarrassment?

Another intriguing question is what kinds of triggers (or combinations) elicit jealousy (which has a sharp edge) as opposed to admiration, other than the fact that the latter elicits emulation without malice, whereas the former motivates depriving the target or resources you wish to acquire. If there are two prizes being offered in a competitive game of skill – one of which the target person has acquired – the result might be admiration motivating parallel acquisition of the remaining prize. On the other hand, if there is only one resource, aggressive acquisition requires motivation via jealousy.

A recurring theme, throughout this essay is the contrast between the “rational” or intuitively “obvious” view, on the one hand, and the actual emotion experienced, on the other; e.g., we suggest that based on common sense, beggar “A” should be more jealous of Bill Gates than of beggar “B.” One might initially expect that since jealousy is motivated by the discrepancy of resource, the larger the discrepancy the more the jealousy, but as we have seen that is not the case. The reason for this again is that it would be a poor strategy, evolutionarily, for a beggar to seriously allocate resources of time and energy to become equal to Bill Gates, when the same resources could be more profitably allocated to the more realistic goal of competing successfully against a neighboring beggar.

As another analogy of the difficulty disentangling different threads of culture, genes, emotion, logic, etc., consider the case of you being jealous of your girlfriend having a fling with a man vs. a woman (assuming she is not a habitual lesbian). Most men in our experience would be more upset by the former. This could be for the obvious reason that a man does not want her to be accidentally inseminated and cuckolded, whereas there is no danger of this with a lesbian fling (again, common sense ought to predict that you ought only to be jealous of the fling that produced more pleasure; the gender of the fling-partner should be irrelevant). An alternative to the EP counter-cuckolding argument would be that the male is regarded as being in an “equivalent class” and elicits a bigger competitive jolt – hence jealousy – than a fling with a woman.

Given how primitive our knowledge of the subtle nuances of human emotions is, it is hardly surprising that our insight into the causes of mental illness – which are primarily disturbances of emotions – is equally primitive. It can hardly be true that all the diverse emotional disturbances of a complex organ like the human brain fall into a handful of categories; mood disorders, psychotic disorders, dissociative disorders, etc. (leaving aside the many hundreds of bogus disorders fabricated to be included in the DSM for insurance purposes).

We believe that a deeper understanding of the functional logic and emotional disturbances that underlie mental illness could be obtained by adopting an evolutionary perspective. As we have discussed in more details elsewhere (see Jalal and Ramachandran, in preparation), we propose that gaining deeper insight into the evolutionary rationale of negative emotions and behaviors (including primitive psychological defense mechanisms) could have therapeutic utility. This approach places emphasis on the evolutionary origins of mental quirks – including pathologically amplified ones – which makes it different from conventional therapeutic techniques. It merges elements of psychoanalysis (by stressing the role of primordial drives and defense mechanisms) and cognitive behavior therapy (CBT; in that it takes the patient step by step through logical “what if” questions) – embedded in an overarching evolutionary theme. Among other strategies, it uses the approach of posing absurdly farfetched dilemmas to get to the axiomatic system of values (and their derangements) that drive your behavior. A striking example is the observation that noticing what or who you are jealous of is often a more “honest” and accurate indicator of what you truly value than simply asking the same question directly to yourself. Once such a deeper understanding is gained you can begin to shake off emotions and behaviors that are overall maladaptive in the current context. This therapeutic approach would supplement rather than negate current psychotherapies and pharmacological approaches.

Ethics Statement

The study included informal surveying of friends and colleagues, and as such was exempt from ethical approval.

Author Contributions

All authors listed have made a substantial, direct and intellectual contribution to the work, and approved it for publication.

Conflict of Interest Statement

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Acknowledgments

We thank Paul McGeoch and David Brang for stimulating discussions. Data were obtained by the second author of this manuscript prior to joining his current institution (University of Cambridge). As the data included informal surveys (opinions), ethical approval or written informed consent was not required in accordance with the national guidelines in Denmark – that is, the country where the data were collected.

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Research topics at the Center for Evolutionary Psychology

Reprints are provided for scholarly purposes only.  Permission to reprint any article must be sought from the holder of the copyright. 

Scientists at the Center for Evolutionary Psychology specialize in finding new ways that an evolutionary perspective can inform research on the design of the human mind.  In so doing, we have been researching many new topics, as well as trying out new approaches to old topics.  Below we provide a partial list with links to some relevant research papers. 

Principles of evolutionary psychology

A roadmap to principles of evolutionary psychology

Reasoning and rationality

Social exchange reasoning (reciprocation, reciprocal altruism, cooperation)

Judgment under uncertainty  (intuitive statistics; optimal foraging; ecological rationality; heuristics & biases)

Adaptationism, normative theories, and rationality

Emotions—What are they?

Emotion  (emotions as super-ordinate programs solving the problem of mechanism coordination in a multimodular mind)

Emotions—Specific ones

Anger . See also:

Formidability, Strength, and Entitlement . Adaptations for detecting physical strength

Vision and Visual Attention

Visual attention –a system specialized for monitoring animals

Vision : Faces—the case for domain-specific object recognition

Evolutionary Biology

Evolutionary Biology : Intragenomic Conflict , Pathogens & the Evolution of Sexual Recombination; Banker’s Paradox (etc)

Literature and the Arts

Art, Fiction, and Aesthetics

Close social relationships

Kin detection  (as regulator of incest avoidance; altruism)

Friendship and Deep Engagement Relationships

Courtship, Mate Choice, and Human Sexuality

Varieties of Cooperation

Two-person cooperation / reciprocation / reciprocal altruism

Evolution of generosity

Cooperating in Groups:

Coalitional psychology and alliance detection

Adaptations for collective action

Memory  (memory systems; specializations; personality trait database; self-knowledge, episodic memories; amnesia; memory loss )

Spatial cognition

Spatial adaptations for foraging (female advantage in location memory for plants; content effects; optimal foraging)

Tools: Cognitive foundations

Adaptations for tool use  (the artifact concept and inferences about function; design stance; problem solving, dissociation between inferences about function and naming)

Personality

Personality (personality differences and universal human nature; adaptationist framework for personality science; cognitive systems specialized for encoding, storing, and retrieving knowledge of personality traits)

The links below are not live yet—hopefully I will be able to update them soon! LC

Darwinian medicine, Darwinian psychiatry

Development

Economics, Business, and Organizational Behavior

Hazard Management (precautionary reasoning)

Intelligence (improvisational intelligence; dedicated intelligence; decoupled reasoning (counterfactual reasoning, suppositional reasoning, metarepresentation)

Theoretical foundations of psychology and the behavioral sciences

Environments of Evolutionary Adaptedness  (EEA; Why the past explains the present)

Evolutionary psychology: A primer

A brief introduction to the field in  [ English ], [ Español ] and [ Português ].

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Essay on evolutionary psychology: top 6 essays | psychology.

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Here is an essay on ‘Evolutionary Psychology’ for class 11 and 12. Find paragraphs, long and short essays on ‘Evolutionary Psychology’ especially written for school and college students.

Essay on Evolutionary Psychology

Essay Contents:

  • Essay on the Principles of Evolutionary Psychology

Essay # 1. Social Behaviour of Apes:

Evolutionary psychology is ripe with examples from the animal world. Usually, a number of species, many of them quite distant to we humans, are used with each species illustrating a basic principle.

Let us depart from this formula by first examining thumbnail sketches of the social organization, mating styles, and aggression of the three great apes that are our genetically closest relatives—gorillas, chimpanzees, and bonobos. By comparing and contrasting the behaviour of these three species, we can illustrate many of the major issues of evolutionary psychology.

i. Gorillas:

A gorilla community is dominated by a single adult male silverback, although sometimes the silverback will allow a good buddy or two to share his reign. The rest of the group consists of several adult females and their juvenile and adolescent offspring. The silverback(s) vigorously defend their harem against the attempts of single males to entice away one or more of the breeding females.

Young adult males almost always leave their natal group and try to gather a harem of their own. Life is tough for the bachelor. He will either wander alone or join several other bachelors and form a group of their own. Gathering a harem is not easy. By dumb luck, an old silverback may die and the closest bachelor, after fending off attempts by rival males, may claim most of the harem.

More typically, however, the male collects a female at a time by challenging a silverback in an established group and luring a female away. As a result, most males do not mate while the lucky few sire a large number of offspring.

Gorilla mating begins when a female enters estrus. In response to hormones, her labia change colour and swell, and the females “present” their bottoms to the adult male(s) of the group. Because of the social structure, the female gorilla mates only with the silverback(s) in the group. In such a system, paternity is assured—if the father is not the dominant male, then it is his best buddy.

Although gorillas are remarkably peaceful in general, males engage in infanticide in two situations. The first is when a male gains a new female or takes over a whole troop. Here, he will often kill all the infants of his new mate(s). The second situation is more insidious. A male may invade an established harem and kill an infant, despite an aggressive defense from the silverback and the infant’s mother.

When this occurs, a strange phenomenon takes place—within a few days, the infant’s mother will abandon her group and take up with the strange male who killed her offspring! While a human mother would plot murderous revenge, the gorilla mother prefers to desert a male who proved incapable of defending her infant in favour of another male who is more likely to protect her future infants. For the killer, this type of infanticide is a tactic to gain a mating female.

ii. Chimpanzees:

Chimps are organized into communities centered on a cadre of adult males. Males remain within the troop into which they are born and forge strong social bonds with one another. They will travel together, groom one another, and aggregate into opportunistic hunting parties.

Although power politics and alliances are a way of life among the males in a chimp community, the males of a group unite against the males in neighbouring communities. They actively patrol their own groups’ territory to prevent incursion, and they form “party gangs” to raid a neighbouring chimp community in order to kill a male or abduct a female.

Females emigrate from their natal community and become associated with another group of males. Females do not bond with other females or with males as strongly as the males of a troop bond to one another, and they live in home ranges that overlap the troop’s territory. In the dominance hierarchy within the group, all the adult males are invariably dominant to the females.

According to Wrangham and Petersona young male “enters the world of adult males by being systematically brutal toward each female in turn until he has dominated all of them. … In a typical interaction, he might charge at the female, hit her, kick her, pull her off balance, jump on top of her huddled and screaming form, slap her, lift her and slam her to the ground, and charge off again.”

Like gorillas, chimp mating begins with estrus and has three forms. The first and most typical form is for the female to mate promiscuously and frequently with virtually every male in her group. In the second form, which often occurs close to ovulation, one of the high-ranking males may form a short-term, possessive bond with the female.

Here, the male will remain close to the female and use combinations of threats and aggression to discourage her from leaving and to prevent subordinate males from copulating. Both the promiscuous and possessive forms can take place within a single estrous period. The third and rarest form is the consortship.

Like gorillas, male chimps may practice infanticide when a new female joins their group with an infant. Males will gang up on the new female and despite her defense, eventually rip the infant away from her, take it to a secluded area, and kill it.

Essay # 2. Human Social Organization and Mating:

To illustrate predispositions and constraints shaped by evolution, let us compare human social organization, mating patterns, and aggression to those of gorillas, chimps, and bonobos. Imagine, for the moment, the college-aged men and women belonging to a human culture that followed the pattern of gorillas.

There could be sororities and fraternities, of course, but they would take a decidedly different form. Each sorority would be small and headed by a mature adult male who would jealously guard his harem and their offspring from contact with any other college male. In order to keep his females under eye, the male would probably demand that they all take the same classes that he takes.

Perhaps two or three different harem groups may share the same classroom, but there would probably be physical barriers in the room to prevent them from interacting. Otherwise, the males would disrupt the class by their displays, posturing, games of one-upmanship, and even overt aggression to prevent any female in their harem from leaving and/or to entice another female into joining their harem.

Each coed would feel that is quite natural to have sex with the male and have him as the father of her children. Although there may be squabbles among the women, there would be no possessiveness or jealousy about sharing him with the others. Both the male and the females may feel physical and perhaps even emotional attraction to one another. However, the concept of casually dating someone else would never even cross anyone’s mind.

Males without a harem would either live solitary lives or join together into an all-male fraternity. Bachelor males could easily take classes with other bachelor males, but to maintain order, the college would prohibit bachelors from taking courses with harems. If a harem master gets a bit long in the tooth, a bachelor will engage in repeated displays of dominance and aggression with him in order to drive him away and take over the women. If the bachelor succeeds, the females will not follow their former mate and father of their children. They will placidly go with the victor, have sex with him, and have his children.

There would be continual games of dominance between the bachelors and a harem male as he leads his harem and children across campus. Sometimes a bachelor might find a female and her infant isolated from the main group. Here, he might grab and kill the infant despite vigorous protests and attacks from the mother.

It may take a few days for the female to get over this event, but soon she would find herself attracted to her child’s killer and will leave her own harem group to join up with him. There would be no charges of murder or any disciplinary action from the university. The bachelor is doing what any reasonable unattached male would do to try to get a mate.

Now imagine a different scenario. Again, let us again consider collegiate life, but this time, one organized on the basis of the chimpanzee. Here, there are no dominant males with their harems. Instead, there would be very strong fraternities with fierce—perhaps even murderous—rivalries among them.

Sororities, if there were any, would have poor internal organization compared to the fraternities. In general, the women would act a bit more as loners while the males would almost always be found with their buds. Each sorority would be strongly associated with a fraternity.

A coed would go through cycles of heat and sexual abstinence. As she enters heat, the guys would pay closer attention to her and quarrel among themselves to get near her. Although she might prefer some males to others, she would find it very natural to have sex repeatedly with all the frat boys.

She must be careful in spurning someone’s advances; if she protests too much, she may be beaten and raped. As ovulation nears, one of the more dominant males might try to sequester her for himself by challenging any subordinate who tries to mate with her. He may be successful for a while, but he usually fails to inhibit her promiscuity—after all, he cannot guard her 24 hours a day. If she becomes pregnant, she will not know who the father was.

Essay # 3. Inclusive Fitness and Kin Selection:

Sometimes, mothering ring-neck pheasants perform a marvelous act of self-sacrifice. If a large animal trod too close to her nest, she will make a great deal of noise and run through the field flapping her wings. The safest course of action for her is to be silent, run a few steps to build up the momentum for flight and then soar away.

Yet she makes herself deliberately conspicuous to a potential predator and is sometimes caught in the process. Prairie dogs also show similar behaviour. When a raptor soars overhead or a land based predator approaches the colony, the prairie dogs who initially spot the threat stand upright on their hind legs and issue a series of loud barks that act as alarm codes for their colony mates to run post haste to their boroughs. This behaviour assists the colony as a whole, but at the expense of making the signaller conspicuous to the predator.

These are examples of altruism, a behaviour that can reduce the reproductive fitness of the altruist but increase the fitness of conspecifics. Ever since Darwin’s time, altruism posed a problem for natural selection. Certainly any heritable behaviour that reduced fitness should decrease over time.

Just consider a prairie dog colony that consists of 50% altruists and 50% cheats. When a cheater spots a predator, he hightails it to the nearest borough. The odds that the predator eats an altruist are slightly increased because the cheater has just removed one of his own kind from the denominator of vulnerable prairie dogs.

When the altruist spies the threat, she announces her position to the predator and places herself in danger. Both the other altruists and the cheaters benefit, but if anyone is to be devoured, it is once again more likely to be the altruist than the cheater.

Using mathematical models, Hamilton showed that altruism could evolve when altruistic genotypes preferentially benefit other altruistic genotypes over cheater genotypes. The clearest way for an altruistic genotype to do this is to have mechanisms that bias it to work altruistically for close genetic relatives.

Hamilton’s work presented the twin ideas of inclusive fitness and kin selection. Inclusive fitness is defined as the fitness of an individual along with the fitness of close relatives. Your inclusive fitness would be a weighted sum of your own reproductive fitness, that of your first-degree relatives, second degree relatives, etc.

Kin selection refers to implication of inclusive fitness that natural selection can work on the close genetic relatives of the organism actually performing the behaviour. In a loose sense, fitness can be expressed in terms of kinships just as we have seen it being expressed in terms of genotypes, phenotypes, and individuals.

Inclusive fitness and kin selection have been used to explain different human behaviours. The very fact that we humans recognize and pay close attention to genealogy may reflect a cognitive mechanism developed through evolution that helps in kin recognition.

The phrase “blood is thicker than water” has been interpreted as a realistic description of human emotions and behaviours that preferentially benefit kin over others. Several aspects of altruistic parental behaviour may have evolved through kin selection. Continual themes in fiction portray noble parents shielding their young children from potential harm, but evil stepparents threatening their stepchildren.

Daly and Wilson have pointed out how familial homicide patterns agree quite well with kin selection. Although rare, parents do murder a child, but the perpetrator of such a heinous act is much more likely to be a stepparent than a biological parent. Despite the hyperbolic threat “do that again and I’ll kill you” echoed by many a frustrated parent, very few parents ever even contemplate homicide when it comes to their offspring. The inhibition of homicide is not restricted to parents and their offspring.

Ask yourself the following two questions – “In your whole lifetime, which person has shouted at you and hit you the most?” and “Which person have you yelled at and fought with the most?” If you respond like most people, then you will nominate a brother or sister. Yet fratricide is very rare. Humans are much more likely to kill a spouse than an offspring or sibling.

Essay # 4. Reciprocity and Cooperation:

A close cousin to inclusive fitness is the concept of reciprocity and cooperation, sometimes called reciprocal altruism. Traditionally, inclusive fitness and kin selection have been used to refer to altruism towards genetic relatives.

Reciprocity and cooperation deal with behaviour that requires some “sacrifice” but also has beneficial consequences between conspecifics who are not necessarily genetic relatives. Hence, the target of the behaviour—a genetic relative versus another conspecific—distinguishes inclusive fitness from reciprocity/cooperation.

To understand reciprocity and the problem it posed for evolutionists, we must once again consider cheaters. Lions and wolves hunt large prey cooperatively. Although it is mentioned infrequently on the nature shows, chasing, grabbing, and killing large prey is not a safe enterprise.

Zebras kick and bite, wildebeest have horns, and caribou have antlers, so predators can be hurt, sometimes even mortally so, in the hunt. Imagine a cheating lioness who approaches the prey only after it is dead. Would not her behaviour be advantageous? She can participate in the feast but avoids the risk of injury.

If cheating has a selective advantage, then would it not eventually result in the extinction of cooperative hunting? Another problem is how cooperative hunting ever got started in the first place. Most feline predators like the lynx, tiger, cheetah, leopard, and jaguar, make a perfectly fine living at solitary hunting. Why did lions ever develop cooperation?

According to Trivers cooperation cannot evolve alone. It must be accompanied with mechanisms that detect and reward mutual cooperators and detect and punish cheaters. Consider grooming in primates. It serves the very useful function of eliminating large parasites (fleas, lice, etc.) from a hairy monkey or ape.

Imagine that you are a chimp and that a fellow chimp, Clyde, is continually presenting himself to you to be groomed. Being the nice chimp that you are, you groom Clyde every time that he requests it. After a while, however, you notice something peculiar. Whenever you present yourself to Clyde for grooming, he refuses.

Ask yourself how you truly feel about this situation and how you are likely to respond to Clyde’s future presentations. Again, if you are like most people, when Clyde presents to you, you would feel some form of negative emotion that could range from mild exasperation to downright contempt, depending on the type of chimp you are. At some point, you are also likely to refuse to groom Clyde. Evolutionary psychologists would say that this is your “cheat detection and punishment” mechanism in action.

Reciprocity evolves when reciprocity and cheating can be recognized or anticipated and then acted upon. If your roommate, Mary, is cramming for her physics exam, you are likely to bake some banana bread for her when you suspect that Mary will do something nice for you on the eve of your big chemistry exam next week.

But if Mary were the type of roommate who clutters and trashes the place leaving you to do all the cleaning up, then you are likely to feel irritated and aggravated at her. No banana bread tonight! We feel that it is right and just that everyone does their fair share, and as parents, we spend considerable time and effort inculcating this ethos into our children.

One of the strengths of the modern evolutionists is their ability to uncover subtle and non-obvious phenomenon that fit better with evolutionary theory than other theory. You were correct to express skepticism of the Mary example— after all, there is really no way to determine the relative influences of a biologically soft wired “cheat detector” and your upbringing on the behaviour. But consider the following example, taken from Pinker.

Essay # 5. Parental Investment:

Robert Trivers, who first explicated reciprocity and cooperation, also gave us parental investment theory. This theory states that in any species the parent (male or female) that invests the most time, energy, and resources on its offspring will be the choosier mate.

The theory begins by asking the fundamental question of why many species act finicky in choosing mates. Most evolutionists explain mate preferences as mechanisms that genes have developed in organisms to assist in their own (i.e., the genes own) replication.

Triver’s theory maintains that the fastidiousness of mate preferences will be stronger in the sex that expends the most resources in producing offspring. Ordinarily, this will be the female because biologists define a female as the sex of a species that produces the larger gamete. The sex that produces the larger gamete produces fewer of those gametes. Hence, each gamete is more “precious” in a reproductive sense.

In mammals, the female expends more resources on offspring than the male. Fertilization in mammals is internal to the female, offspring development takes place in the female’s uterus, and the female must suckle the infant for a significant period of time. Hence, female mammals should be choosier mates than the males. Indeed, this is always the case.

In species where one sex competes for mating, males compete with other males for the opportunity of having sex with females. Females do not butt heads with each other for the opportunity of mating with any random guy in the herd.

Even in chimps and bonobos, where mating is largely promiscuous, every male in a troop tries quite hard to have a go at any female in estrus. Whenever one sex shuns a mating attempt, it is the female shunning a male and not a male shunning a female.

Parental investment theory, along with the concept of certainty of parenthood, has been used to explain many different types of human mate preferences. Females must commit nine months to pregnancy and then, before the advent of manufactured baby formula, more than a year to feeding a single offspring.

Even if a woman conceived after her first menstruation, she could bear one child per year until menopause, and the most likely number of offspring for a female during most of human evolution was probably no more than five. A human male, on the other hand, has the potential of fathering a baby every single day after puberty.

Female humans are biologically constrained to devote considerable resources to a single offspring; human males lack such constraints. Hence, human females should have more discriminating mate preferences than males.

A litany of empirical observations is used to support of this conclusion. Certainly in our Western cultures, anecdotal observations agree with it. Males are more ready than females to engage in anonymous sex, even to the point of paying for it. Women report more sexual advances made on them by men than men report sexual advances initiated by women.

Consider the following questions—how long would you have to know someone before feeling comfortable going out on a date with that person, and how long would you have to know someone before getting married? Both males and females have similar time frames—a short time frame for dating and a longer one for matrimony.

Now consider this question—how long would you have to know someone before having sex? The average woman picks a time frame somewhere between dating and marriage. Males pick a time frame shorter than dating.

This account of human parental investment, however, faces a real problem—why should men ever stick around at all? If sleeping around with as many women as possible maximizes the reproductive fitness of the genes in a male organism, why would these genes ever develop mechanisms that predispose a man to settle down with a woman? The evolutionists answer to this is that it effectively “takes two to tango.”

Just like the peacock’s tail, men’s behaviour is influenced by women’s mate preferences. If mutations arose that influenced women to prefer men who stuck around, and if there were men who actually did stick around, and if the pairing between this type of woman and this type of man had high reproductive fitness, then females who prefer stabile males would increase in frequency as will males who actually remain stabile.

Essay # 6. Principles of Evolutionary Psychology:

Several decades ago, American psychology held several laws of learning as sacred. One law was equipotentiality and it stated that an organism could learn to associate any stimulus to any response with equal ease. The classic example is Pavlov’s dog who, according to this law, could have learned to associate a bright light to the food as easily as it learned to associate the bell with food.

The two stimuli, light and bell, are equipotent in the sense that given the same learning parameters, both could eventually lead the dog to salivate. A second law was temporal contiguity. This law stated that the presentation of a novel stimulus with a learned stimulus must occur quickly in time. In Pavlov’s case, the food must be presented shortly after the bell was rung in order for learning to occur.

The dog never would learn to salivate to the bell if the food were presented three days after the bell. The third and final law was practice—it took many trials before the behaviour was fully learned.

These laws begin to crumble after a series of fortuitous studies in the 1950s and 1960s by the psychologist John Garcia and his colleagues. Garcia’s initial interest centered on the behavioural effects of low doses of radiation.

In the experimental paradigm, rats were placed into a special chamber for a relatively long time while they were exposed to a constant amount of low level X-ray radiation. To keep the rats healthy, the chamber was equipped with water bottles containing saccharin-flavoured water.

Garcia and his colleagues noticed three important things:

(i) As expected, the rats became sick from the doses of X-rays;

(ii) Quite unexpectedly, the rats stopped drinking the sweetened water; and

(iii) The rats needed no practice to avoid the water—they learned after one and only one trial.

Garcia’s genius consisted in asking one simple question, “Why should these rats avoid drinking the water when the learning situation violated the accepted laws of learning?” According to the Pavlovian tradition, the unconditioned response (sickness) occurred several hours after the conditioned stimulus (sweetened water).

This clearly violated the law of temporal contiguity because the paring of sweetened water and sickness did not occur within a short time interval. Second, there was no need for practice. Most rats learned to avoid the water a single trial.

Garcia abandoned his initial interest in radiation poisoning to focus on this peculiar phenomenon of learning. His general results and conclusions are illustrated by the study of Garcia and Koelling. Here, rats were assigned to one of four groups in a two by two-factorial design.

The first factor was the sensory quality of water given to the rats—it could either be coloured with a food dye and oxygenated with bubbles (coloured, bubbly water) or mixed with saccharin (sweetened water).

The rats in the coloured, bubbly water/shock group eventually learned to avoid drinking the water, albeit after a number of trials. This accords well with the established laws of learning at the time. Rats shocked after drinking sweetened water, however, failed to learn avoidance within the time limit of the study. This fact clearly violated the established law of equipotentiality under which sweetness should lead to just as much avoidance as the visually coloured water.

Curiously, the effect of making the rats sick had showed the opposite pattern. Rats made sick by the coloured water had a difficult time learning to avoid it while rats sickened by lithium learned to avoid the water after one trial. The coloured-water/lithium group followed the established laws of learning because sickness did not occur in temporal contiguity with the water. The sweetened-water/ lithium group, on the other hand, violated the laws just as much as those rats made sick by X-rays did.

The current explanation for this curious state of affairs is that the laws of learning depend importantly on the biological predisposition of a species. The rat has evolved into a highly olfactory creature that perceives the world in terms of smell and taste. Indeed, rat colonies develop a characteristic smell that is used to recognize colony mates and identify intruders.

Rats are also scavengers who dine on a surprisingly wide variety of organic material. Because they locate food though smell, they are especially attracted to rotting fruit, vegetable, and animal matter because of its pungent odour. Rotting food, however, poses a problem for digestion because it can create sickness when it is too far gone.

Rats react to their food in a peculiar way. When a rat locates a novel food source, he seldom gobbles it all up. Instead, he will nibble a little bit of it, go way for several hours, and then return. The rat may repeat this another time or two—a quick taste, a lengthy departure, and then a return—but soon he will return and gorge on the food.

Interestingly, if an experimenter laces the original food source with enough poison to make the rat sick but not enough to kill him, the rat may return but will not eat the food any more. It is usually a quick, one trial learning experience.

Evolutionary psychologists speculate that rats evolved a biological predisposition and a behavioural repertoire to avoid rotting foods that may make them ill. At some point rats that nibbled at a novel food source out-reproduced those who gobbled the whole thing down, presumably because the gobbling strategy had a high probability of incapacitation or even death through sickness.

Similarly, rats who nibbled and learned quickly out-reproduced those who nibbled but took a long time to learn. And what sensory cues would the rat use to bad food from good food? Most likely they would be olfactory cues.

In this way, rats in the Garcia and Koelling study would easily learn to associate an olfactory cue (water sweetness) with eventual sickness but would have a harder time associating a visual cue (coloured, bubbly water) with sickness. Rats who learned to avoid sweetened water when they became sick were biologically predisposed to learn this and to learn it quickly.

Proponents of this interpretation of the data are quick to point out the role reversal that happens in different species. Birds, who are highly visual like us humans, associate visual cues with sickness with the ease that rats learn about olfactory cues and illness. Birds will readily learn to avoid, say, blue food pellets and eat red pellets. When presented with a novel pellet that is half blue and half red, the bird will peck at the middle, break the pellet in two, and then eat the red half.

The general phenomenon has now come to be called prepared learning or biological constraints on learning, a hypothesis that was initially proposed in 1911 by the famous learning theorist, E.L. Thorndike, but was ignored by later researchers. The prepared or constrained part of the learning process is due to the biology that has been evolutionarily bequeathed to a species.

Human Fears and Phobias From the perspective of evolutionary psychology, fear and panic—like most of our emotions—should be viewed as adaptive responses. They may be unpleasant to experience, but they serve the useful function of prompting us to avoid dangerous situations and/ or to energize our bodies for fight or flight.

The relationship between fear and adaptiveness resembles the inverted U- shaped function of stabilizing selection. In general, it is good to be in the middle of distribution. Too little fear could lead to maladaptive risk-taking while too much fear might incapacitate a person.

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Scientific Strengths and Weaknesses of Evolutionary Psychology - Essay Example

Scientific Strengths and Weaknesses of Evolutionary Psychology

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Psychology Essay Topics

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Published on: May 2, 2023

Last updated on: Jan 30, 2024

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Are you struggling to come up with interesting and unique psychology essay topics? Do you find it challenging to write a compelling psychology essay that stands out from the rest?

Psychology is a fascinating subject. However, selecting a topic that is both engaging and informative can be a daunting task.

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Psychology Research Topics For High School Students

Here is a persuasive essay topics list to get you started:

  • The influence of social media on mental health
  • The psychology of dreams and their interpretations
  • Effects of stress on academic performance
  • Does childhood trauma impact mental health in adulthood, and if so, how?
  • How does meditation impact the brain and promote well-being?
  • Why do we make the choices we do, and how can we make better decisions?
  • How does spending time in nature impact mental health and well-being?
  • How does perception affect our interpretation of reality, and can it be changed
  • The power of music on human emotions and behavior
  • The relationship between exercise and mental health

 Psychology Paper Topics For College Students

  • The psychology of addiction and effective treatments.
  • The impact of childhood experiences on adult mental health.
  • The psychology of prejudice and how to overcome biases.
  • The role of emotions in decision-making and behavior.
  • The effects of sleep deprivation on cognitive function and well-being.
  • Effective leadership traits and development.
  • The psychology of procrastination: Why we do it and how to overcome it.
  • The impact of social support on mental health.
  • The effects of mindfulness on stress and anxiety.
  • The psychology of motivation: What drives our behavior and how to stay motivated.

Research Topics In Psychology For University Students

  • The effects of social media on self-esteem and body image.
  • The impact of childhood trauma on brain development and function.
  • The psychology of happiness: What makes us happy and how can we cultivate it?
  • The role of genetics in mental health disorders and treatment implications.
  • How does social media affect self-esteem and body image?
  • What is the impact of childhood trauma on brain development and function?
  • What makes us happy and how can we cultivate happiness?
  • The psychology of mindfulness: Benefits and applications for well-being.
  • The impact of cultural differences on cognitive processes and behavior.
  • What are the dynamics of attraction, attachment, and relationships in the psychology of love?

Social Psychology Essay Topics

  • How do social roles and expectations affect behavior?
  • What is the role of social identity in intergroup relations?
  • How do attitudes and persuasion shape behavior?
  • What are the psychological factors that influence conformity?
  • What is the impact of social comparison on self-esteem?
  • The influence of culture on social behavior
  • The role of empathy in social interactions
  • The impact of social exclusion on mental health
  • The effects of social comparison on body image
  • The psychology of altruism and helping behavior

Forensic Psychology Essay Topics

  • How can forensic psychology contribute to criminal profiling?
  • What is the impact of psychological factors on criminal behavior?
  • How do juries make decisions in criminal cases, and what role does psychology play?
  • What is the impact of false confessions on the criminal justice system?
  • How can forensic psychologists help prevent and treat juvenile delinquency?
  • The psychology of criminal behavior and decision-making
  • The use of psychological assessment in criminal trials
  • The role of media in shaping public perceptions of crime
  • The impact of trauma on criminal behavior
  • The psychology of witness testimony

Criminal Psychology Essay Topics

  • How do psychological factors contribute to the development of criminal behavior?
  • What is the impact of childhood experiences on criminal behavior?
  • How can criminal psychology contribute to the prevention and treatment of criminal behavior?
  • What is the relationship between mental health and criminal behavior?
  • How can criminal profiling be used to aid criminal investigations?
  • The psychology of white-collar crime
  • The use of forensic psychology in criminal investigations
  • The impact of incarceration on mental health
  • The effectiveness of rehabilitation programs for offenders
  • The psychology of recidivism

Cognitive Psychology Essay Topics

  • How do cognitive processes shape our perceptions and decisions?
  • What are the neural mechanisms underlying cognitive processes such as attention and memory?
  • How do emotions and motivation affect cognitive processing?
  • What is the relationship between language and thought?
  • What is the impact of cognitive biases on decision-making?
  • The role of cognitive development in learning and education
  • The impact of technology on cognitive processing
  • The psychology of creativity and problem-solving
  • The effects of sleep on cognitive function
  • The psychology of expertise and skill acquisition

Developmental Psychology Essay Topics

  • How do genetics and the environment interact to shape development?
  • What are the stages of cognitive and emotional development in childhood and adolescence?
  • What is the impact of parenting styles on child development?
  • How do cultural differences impact child development?
  • What are the effects of early adversity on later development?
  • The psychology of attachment and bonding
  • The impact of technology on child development
  • The effects of divorce and separation on child development
  • The psychology of adolescent identity development
  • The role of play in child development

Abnormal Psychology Essay Topics

  • The impact of childhood trauma on the development of dissociative disorders
  • The role of genetics in the development of schizophrenia
  • The link between eating disorders and body image dissatisfaction
  • The impact of addiction on mental health
  • The effectiveness of psychotherapy for treating personality disorders
  • The relationship between anxiety and depression in bipolar disorder
  • The impact of trauma on the development of obsessive-compulsive disorder
  • The role of cognitive-behavioral therapy in treating phobias
  • The impact of culture on the diagnosis and treatment of mental illness
  • The effectiveness of mindfulness-based therapies for treating anxiety and depression

Child Psychology Essay Topics

  • The impact of attachment styles on child development
  • The role of play therapy in treating childhood trauma
  • The impact of parenting styles on adolescent mental health
  • The role of technology in children's social and emotional development
  • The impact of peer relationships on child development
  • The effectiveness of early intervention for children with autism spectrum disorder
  • The impact of divorce on child development
  • The role of schools in supporting children's mental health
  • The impact of childhood bullying on mental health in adolescence and adulthood
  • The effectiveness of family therapy in treating childhood anxiety and depression

Sports Psychology Essay Topics

  • The role of mental toughness in athletic performance
  • The impact of anxiety on sports performance
  • The relationship between goal setting and athletic success
  • The impact of visualization techniques on sports performance
  • The role of self-talk in athletic performance
  • The impact of team cohesion on athletic performance
  • The relationship between personality traits and sports performance
  • The impact of pre-performance routines on sports performance
  • The role of coaching in supporting athletes' mental health
  • The effectiveness of psychological skills training in improving athletic performance

Argumentative Psychology essay topics

  • Is intelligence innate or acquired?
  • Should psychotherapy be used as a first-line treatment for mental illness?
  • Is the use of medication in treating mental illness over-prescribed?
  • Is social media use linked to increased rates of anxiety and depression?
  • Is addiction a disease or a choice?
  • Should personality disorders be treated differently than other mental illnesses?
  • Is the use of restraints ethical in mental health treatment?
  • Is it ethical to use animals in psychological research?
  • Should parents be held responsible for their children's mental health?
  • Is there a link between childhood trauma and criminal behavior?

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Descriptive Psychology Essay Topics

  • The history and evolution of psychoanalytic theory
  • The role of culture in shaping our understanding of mental illness
  • The impact of attachment theory on contemporary psychology
  • The development of cognitive psychology as a discipline
  • The role of social psychology in understanding human behavior
  • The impact of behaviorism on modern psychology
  • The role of neuroscience in understanding mental illness
  • The development of positive psychology as a field
  • The impact of feminist psychology on contemporary practice
  • The role of evolutionary psychology in understanding human behavior

Biological Psychology Essay Topics

  • The role of genetics in addiction and substance abuse
  • The impact of hormonal changes on mood disorders
  • Neural mechanisms underlying decision making
  • The effect of sleep deprivation on brain function
  • The link between brain development and mental health disorders
  • The role of neurotransmitters in regulating emotions and behavior
  • The impact of stress on the immune system
  • The relationship between diet and brain function
  • The biological basis of schizophrenia
  • The role of epigenetics in mental health disorders

Controversial Psychology Essay Topics

  • The Ethics of using placebos in clinical trials
  • The Validity of repressed memories in Therapy
  • The controversy surrounding conversion therapy
  • The debate over the existence of multiple personality disorder
  • The controversy surrounding the use of medication to treat ADHD
  • The ethics of using animals in psychological research
  • The controversy surrounding the validity of personality tests
  • The debate over the use of cognitive enhancement drugs
  • The controversy surrounding the diagnosis of borderline personality disorder
  • The debate over the use of hypnosis in therapy

Cultural Psychology Essay Topics

  • The impact of cultural values on mental health treatment
  • Cross-cultural differences in emotion regulation
  • The role of cultural norms in shaping attitudes towards mental health disorders
  • The impact of acculturation on mental health
  • The role of cultural values in shaping parenting styles
  • Cross-cultural differences in attachment styles
  • The influence of culture on body image and eating disorders
  • The impact of cultural values on the experience of depression
  • The role of culture in shaping perceptions of happiness
  • The impact of cultural diversity on group dynamics

Good Psychology Essay Topics

  • The importance of social support for mental health
  • The benefits of mindfulness meditation for stress reduction
  • The role of exercise in improving mental health
  • The impact of gratitude on well-being
  • The role of humor in coping with stress
  • The benefits of nature exposure for mental health
  • The impact of social media on mental health and well-being
  • The benefits of expressive writing for emotional processing
  • The role of positive self-talk in building resilience
  • The impact of volunteering on mental health and well-being

Exciting Psychology Essay Topics

  • The psychology of thrill-seeking behavior
  • The impact of virtual reality on behavior and cognition
  • The relationship between music and mood
  • The psychology of conspiracy theories
  • The impact of social comparison on self-esteem
  • The psychology of persuasion and influence
  • The role of culture in shaping perceptions of beauty
  • The psychology of color and its effects on behavior
  • The impact of humor on creativity and problem-solving
  • The psychology of flow and peak performance

Psychology Essay Topics on Dreams

  • Why do we dream? The scientific and psychological explanations.
  • Can we control our dreams? The effectiveness and limitations of lucid dreaming.
  • The interpretation of dreams: Freudian theory vs. modern approaches.
  • The role of dreams in problem-solving and creativity.
  • How dreams impact our mental health and well-being.
  • The use of dream analysis in therapy: Benefits and limitations.
  • Nightmares: Causes, effects, and treatments.
  • The cultural significance of dreams and dream interpretation.
  • Sleep disorders and their impact on dreaming.
  • The ethical considerations of using dream manipulation for personal gain.

Psychology-Related Topics from Other Subjects

  • The intersection of psychology and neuroscience
  • The relationship between psychology and economics
  • The psychology of decision making in politics
  • The psychology of leadership and organizational behavior
  • The impact of technology on social psychology
  • The psychology of marketing and consumer behavior
  • The relationship between psychology and law
  • The psychology of education and learning
  • The impact of environmental factors on behavior
  • The psychology of creativity and innovation

 Psychology Paper Topics for Any Assignment

  • The influence of video games on cognitive development
  • A case study analysis of borderline personality disorder
  • The role of cognitive psychology in treating depression
  • Historical perspectives on the evolution of cognitive psychology
  • Analyzing the impact of social media on mental health
  • An exploration of the psychology behind addiction
  • A comparative analysis of Freudian and Jungian theories of personality
  • Investigating the effects of mindfulness on anxiety disorders
  • The role of positive psychology in promoting well-being
  • A case study on the effects of childhood trauma on adult mental health
  • Examining the link between physical health and mental health
  • An overview of various psychological disorders and their treatment options
  • The role of cognitive-behavioral therapy in treating anxiety
  • Analyzing the use of art therapy in treating mental health disorders
  • The impact of culture on mental health and well-being

How To Choose A Psychology Topic?

Choosing a psychology topic can seem daunting, but there are some helpful steps you can take to make the process easier. 

Here are some tips to consider:

Identify Your Interests

Start by considering what topics in psychology interest you the most. Are you fascinated by abnormal psychology, cognitive psychology, or social psychology? 

By choosing a topic that you are interested in, you are more likely to be motivated to research and write about it.

Consider The Assignment Requirements

If you are choosing a topic for a specific assignment, make sure to read the instructions and guidelines carefully. Consider the length of the assignment, the required sources, and any other specific instructions that the professor may have provided.

Do Some Preliminary Research

Once you have identified your interests and considered the assignment requirements, start doing some preliminary research. Look for articles, books, and other resources on your topic to get a sense of what has already been written about it and to help refine your focus.

Narrow Down Your Topic

After doing some preliminary research, you may need to narrow down your topic. Try to focus on a specific aspect of the broader topic that you are interested in. This will help you to stay focused and write a more cohesive and effective paper.

By following these steps, you can choose a psychology topic that is interesting, manageable and meets the requirements of your assignment.

 Tips To Write a Compelling Psychology Essay

Writing a good psychology essay requires attention to detail, critical thinking, and clear writing. Here are some tips to help you write a great psychology essay:

  • Understand The Essay Prompt

Make sure you fully understand the prompt before you start writing. Identify the key terms and concepts and make sure you have a clear understanding of what is being asked of you.

  • Conduct Thorough Research

Conduct thorough research using reliable sources such as academic journals, books, and reputable websites. Be sure to take detailed notes and keep track of your sources.

  • Organize Your Thoughts

Organize your thoughts and ideas before you start the writing process. Create an outline or a mind map to help you structure your essay and ensure your ideas flow logically.

  • Use Clear, Concise Language

Use clear, concise language to convey your ideas. Avoid using jargon or technical terms unless necessary, and make sure your sentences are well-structured and easy to understand.

  • Support Your Arguments

Use evidence to support your arguments and claims. This could include citing research studies or other sources to back up your points.

  • Edit and Proofread

Edit and proofread your psychology research paper to eliminate errors and ensure your writing is polished and professional. Check for grammar and spelling mistakes, and make sure your formatting and referencing are consistent and accurate.

By following these tips, you can write a compelling psychology essay that effectively communicates your ideas and arguments.

In conclusion, choosing a psychology essay topic can be a daunting task. But with the right approach, it can be an enjoyable and rewarding experience. 

Consider your interests, current events, and the audience when selecting a topic. Be sure to conduct thorough research and organize your ideas before writing. 

Additionally, keep in mind the tips for writing a compelling essay and crafting a strong thesis statement.

At CollegeEssay.org, we understand that any psychology course can be challenging, especially when you have to write an essay about it.

That's why we offer top essay writing service to help you score good grades.

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Visit CollegeEssay.org to learn more about our psychology essay writing service and how we can assist you in achieving academic success.

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essay topics for evolutionary psychology

Evolutionary Psychology: Depression Essay

Introduction, what is depression, evolutionary psychology and depression.

Man has always been viewed as a social being and his interaction with others plays a very pivotal role in his personal growth and development. According to Keen (2002), man’s need to feel a connection with others is so intense that he will go to great extents, including having make-believe friends just to feel connected.

It can therefore be stated that man cannot wholesomely exist in solitude and his encounter with others, be it by chance or otherwise is very important for his well being. It is due to this fact that depression which at times threatens to infringe mans well being has to be given due consideration.

In this paper, I shall aim to expound on the meaning of depression all the while using psychological underpinning to explore its origin and probably effects be they adverse or otherwise.

Depression can be deemed as a form of mental disorder that brings about feelings of isolation, guilt, a general loss of interest, a decrease in self-worth and suicidal tendencies (Keen, 2002). These feelings are often accompanied by the feeling of emptiness. It should be noted that this isolation need not be physical in nature but can also be emotional.

Contrary to popular belief, depression does not necessarily equate to being lonely and hence it would be perfectly non-contradictory for a depressed individual to describe him/herself as not being lonely. This perhaps stems from the fact that while depression simply implies being emotionally low, it has a physical and mental side and hence is more of a state of mind and needs psychiatric interventions if the patient is to recover fully.

By definition, Buss (2005) describes evolutionary psychology as one of the many biological approaches used by psychologists in a bid to further our understanding on human behavior.

According to the author, all bodily functions are organized and designed to serve the purpose of survival and reproduction. In this regards, it can be argued that cognition too, has a structure that help in the attainment of these purposes and that this functional structure has been developed over time as a result of natural selection.

Bearing this in mind, Buss (2005) asserts that evolutionary psychology has its focus on the evolutionary properties of the human nervous system. To further explain this, the author states that all tissues in the human physiology are functionally interconnected so as to fulfill the key purposes (survival and reproduction) and that this organization of tissue functions is an evolutionary process rooting from natural selection.

This means that the brain is also functionally organized and connected to other body functions and that it can therefore be best explored by applying evolutionary perspectives.

With such underpinnings, it can equivocally be stated that the brain should not be viewed as an organ with a single function but rather, as a collection of functional parts serving psychological adaptations (functions) designed to serve survival and reproduction.

As such, using the ideas formulated by evolutionary psychologists, it makes sense to argue that human behaviors are as a result of psychological adaptations that evolve in a bid to cope with the environment, social and economic settings among others. In addition, evolutionary psychology seeks to portray human nature as an evolving concept based on the ability of human beings to adapt to recurring problems present since the ancestral days.

The best theory that can be used to link evolutionary psychology to depression is the rank theory. As Stevens and Price (2000) explain, the rank theory depicts depression as “an adaptive response to losing rank and conceiving of oneself as a loser Stevens & Price, 2000 p.56).” As such, depression adaptively serves as a tool to facilitate loosing all the while giving humans a chance to accept the fact that they have lost or failed in certain avenues.

Once an individual accepts defeat or submits to failure, an internal process comes into play acting in an inhibitory capacity. This process leads to the common symptoms that are currently used to identify depression. They include but are not limited to: loss of energy, mood swings, guilt, sleep disorders and a sudden loss of appetite, reduced self-worth among others.

There exist a myriad of functions served by depression. Key among them is an evolved capacity among individuals to recognize and accept difference in ranks held by people in a given social grouping. This has not only decrease aggressiveness among humans but has also enabled the human race to establish a system that ensures that the strongest have precedence in accessing various amenities (food, mates and territory) in society.

Looking at social interactions among the Homo sapiens of days past, living in a community provided security, food and shelter security and reproductive success. In today’s society, these values still hold true since each individual desires these aspects and having them gives them a sense of belonging that is integral to the physical and mental wellbeing.

As such, having a rank or commanding a high level of respect are desirable attributes that bring about peace and happiness while being unpopular and rejected by others bring misery and disaster to an individual. The later often lead to depression.

Using the rank theory, Stevens and Price (2000) assert that depression evolved from the concept of yielding which was and still is part of a conflict. Yielding played an pivotal role in ritual conflicts as it ensured that the yielder acknowledged defeat and could therefore not attempt a comeback and at the same time, ascertained to the winner that the yielder had given up thereby showcasing the winner’s dominance and rank in society.

Depression can be caused by the demise of a friend, a visitation by tragedy, the feeling that one does not belong to some social circle amongst other reasons. However, whatever the reason for depression, it eventually visits each one of us at some point in time.

Buss (2005) reaffirms this point by quite boldly stating that depression is in fact inevitable to human beings and as such, should be viewed as a river we will all have to cross at some time. These sentiments further support the fact that depression is an adaptation that has and will continue to evolve through time.

Depression affects all human beings at various points and as such is a subject worthy of some consideration. From the discussion above, depression has been portrayed as an evolving adaptation that is integral to maintaining balance in society.

In addition, a brief overview of evolutionary psychology has been offered and the main underpinnings forwarded by this branch of psychology have been used to explain the origin and nature of depression. Even though it is still a relatively new branch of psychology, it provides scholars with a new angle through which different behavioral studies can be merged and understood.

Buss, D. (2005). The handbook of evolutionary psychology. New Jersey: John Wiley and Sons.

Keen, E. (2002). Depression: self-consciousness, pretending, and guilt . CA: Greenwood Publishing Group.

Stevens, A., & Price, J. (2000). Evolutionary psychiatry: a new beginning . New York: Routledge.

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  23. Evolutionary Psychology: Depression

    In addition, evolutionary psychology seeks to portray human nature as an evolving concept based on the ability of human beings to adapt to recurring problems present since the ancestral days. The best theory that can be used to link evolutionary psychology to depression is the rank theory.